"Poorly equipped" really depends a lot on the context and scale. Like most belligerents in the war, the Japanese did have plenty of glaring deficiencies in equipment in WW2, but they also had several areas where they excelled. At times they were better equipped than the forces they went up against - particularly in China and early in the war in Malaya and the Philippines - while later in the war they became more outclassed.

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If you're referring to general infantry, their shortcomings came in a variety of areas, although the biggest problems tended to be in less visible areas like logistics and artillery. Though it predates Japanese involvement in WW2, the Battle of Khalkhin Gol does a good job really bringing to light these deficiencies compared to a Red Army that still had yet to recover from Stalin's purges. Despite having a railhead half a day's drive from the front (as opposed to the Soviet/Mongolian railhead that was four days away), the IJA suffered from major logistical difficulties as fighting intensified and even had their artillery forces start to run out of ammunition. The Soviets, on the other hand, at the same time managed to send in huge numbers of troops to outnumber the Japanese, support overwhelming numbers of aircraft, and set up an artillery barrage that not only completely outgunned the Japanese, but even intensified even as the Japanese were running out of ammunition. A lot of this stemmed from the comparative lack of motorization among the Japanese army, which very much limited their strategic mobility away from rails. The artillery duel also brought to light how outclassed IJA field artillery was - the Soviets possessed some of the best field artillery pieces in the world at the time, while the Japanese were working with antiquated WW1-era pieces.

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In terms of more local weapons, it was more of a mixed bag. Their tanks were infamously terrible, arguably the worst of any major belligerent in the war. Again looking back to Khalkhin Gol, where the Japanese had their only major tank operation, they had an assault coordinated with infantry stopped by Soviet armored cars and a rifle company. In the Pacific, their tanks were few and far between and massively outclassed compared to Allied armor, and their anti-tank guns were both inadequate for the newer tanks they were pitted against and not available in large enough numbers. Anti-aircraft guns also a major shortcoming, with their 25mm gun suffering from a poor fire rate and traverse speed and generally being inferior to the 40mm Bofors mount being used by the Allies. Just as critically, they lacked the kind of antiaircraft fire control and proximity fuse ammunition that made American antiaircraft fire so devastatingly effective.

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On the level of infantry combat, things were a bit more even, though there were still shortcomings in equipment. Both the Type 38 and Type 99 rifles were excellent bolt-action rifles, but they're still bolt-action, meaning they (like every other bolt-action rifle of the war) were going to be outclassed by a reliable semiautomatic like the American M1 Garand. Their light machineguns were a mixed bag but generally good guns - the Type 11 was the oldest and relied on a hopper feed system that was prone to causing problems, but the more conventional Type 96 and Type 99 machineguns were excellent weapons that were arguably better than their US counterpart, the BAR. Their heavy machinegun was an air-cooled Hotchkiss (Type 3 and Type 92) that was inferior to the GPMGs of the Germans but otherwise perfectly good in its intended role. Their big shortcomings here were in weapons for close combat and again, logistics. Japan ran into the same problem Italy had entering WW2 in that they had made the decision to switch to a new cartridge on the eve of war. The Japanese felt the 6.5mm cartridge of the Type 38 rifle and Type 11 and 96 machineguns was too weak, so they developed a new 7.7mm cartridge along with a new complement of weapons. While the weapons for either cartridge are otherwise fine, the Japanese couldn't rearm fast enough to pull 6.5 from service, and thus were stuck fielding two separate types of, for all practical purposes, identical ammunition through the end of the war. Close combat weapons were a problem because of a major lack of submachineguns. Japan seemed to have little interest in submachineguns leading up to WW2, and no serious effort was put into developing one until it was too late. The only machinegun they ever issued in any real quantity was the Type 100, which was a quick adaptation of the WW1-era MP18 design. It was chambered in the anemic 8mm Nambu cartridge, and it suffered from major reliability problems. It wasn't as streamlined for production as many of the more famous designs of the war like the Sten or PPS-43, and, coupled with Japan's poor industrial capacity and late development of the gun (entering service in 1942), few actually made it to the front.