I haven't seen a note like that in a while--my uncle had a 1-cent and 5-guilder version. It's not from Australia; it's from Japan and issued under the Japanese occupation authority in the then-Dutch East Indies. It says, very unsurprisingly, "The Japanese Government pays to the bearer [on tender] One Guilder."

There were at least two different issues of occupation money, one in guilders (the earlier, in 1942) and one in rupiah (later, in 1944-45), with the second aimed at the fiction of the 'Co-prosperity sphere' and the idea of more local authority to please useful Javanese nationalists in particular, even though the Japanese military occupation still served as guarantor and Japan had no serious plans to hand over control. Those later notes were printed in Djakarta (Batavia). The Dutch government-in-exile also printed money, and all of these were currencies specific to the Indies, not otherwise interconvertible. It was a matter of significant confusion that, along with Japan's own economic problems, created financial collapse around the end of the war, as this was ultimately fiat currency that existed in several different modes, and all were legal tender.

M. C. Ricklefs' A History of Modern Indonesia 4th ed (2008) is the source for general information, but specific matters of money circulation and format from Tracy Schmidt, ed., Standard Catalog of World Paper Money, General Issues, 1368-1960, 16th ed. (2016). It's one of the standard works. The Wikipedia page for Japanese issued currency in Java also has images of most of the bills, including that one. It would have been quite easy to get at the end of the war, I reckon.