It's duty in Japan for employers to withhold tax from your income. When you work as an English teacher in Japan, the employer's duty could be exempted under these conditions : 1. you work there within two months, 2. the employer pay you by the day (but it must not be over 9600 yen). Most important point is that the decision is in the employer's hand. I hope you enjoy your work!
By the way, here's a translation of the question:
English - I’m an English teacher. Do I have to pay withholding tax in Japan? Is it deducted (automatically) from my salary?
Hope this helps!