Macbook AIr Japanese does not work

I'm using MacBook Air running OS X Yosimite. Recently my Japanese keyboard does not work correctly. Sometimes even it's in Japanese mode, I cannot type Japanese and I have to restart the laptop in order to use it again. It does not switch to other modes, the keyboard is still in Japanese when this happens. I did try to change to other keyboard modes, then switched back to Japanese but did not work. Does anyone know how to fix this issue?

Thank you!