[Tsuwabuki]

This depends on so many factors. I have mine, it took me a lot of pain, a lot of effort, and a lot of money. Not to mention taking the test four times before I passed.

...my Australian coworker? He just walked in, and they handed him one.

It depends largely on if your country or state has an agreement with the Japanese government. Australia has like six states. Very easy. America, of course, has more than fifty distinct license granting regions (not just the states, but commonwealths, territories, yadda yadda).

You can drive for a year on your international drivers permit, but after that you need a license. Better find out if your country has an agreement with Japan, if it doesn't, be prepared to pay out the ear, every time you fail, you have to try again, and pay again.