Obtaining a driver's license can be an expensive and frustrating experience, and doing so in Japan is no different in that regard. But for many foreign residents in Japan, transferring their home license into a Japanese one can be a fairly simple and inexpensive procedure, while for others it's an advisable course given the limited validity of an international license here.
For foreign residents who use an international driver's license in Japan, the rules are clear. You can drive legally with this license for one year after you come to Japan, provided your international license remains valid within that period. After that time, if you plan to stay in Japan, you're expected to convert your home country license into a Japanese one.
The meaning of "one year" is taken as one year from the traveler's first date of entry into Japan, or until the license expires. You cannot renew your international license after one year unless you leave Japan for over three months.