You are authorized to work in Japan to engage in the activity permitted under your visa until the date of expiry.

If you wishes to change your job to engage in the similar type of your current activity under another employer,you may file an application for “Certificate of Authorized Employment”for the purpose of confirmation ,on whether or not your intended activity may fall under your current visa.
This certificate is issued by the Immigration Bureau in case your new activity is judged to be fall under your current work visa.
If you wish to obtain this certificate upon the change of your job,you may apply for its issuance by showing the type of your activity authorized to you,at the nearest Immigration Bureau.
Once you obtain this certificate,there will be no concern about your eligibility to work under the new employer and your visa extension will be approved more smoothly.