Having a residence card does not mean you can work

In order to work in Japan, you must have a residence status that allows you to work or be granted permission to engage in activities other than those permitted under the status of residence. If you are an international student or dependent wish to work part-time, you must obtain a permission to engage in activities other than those permitted under your status of residence. “Permission for activities outside the scope of status of residence” “Shikaku-gai Katsudo Kyoka” is required. However, with this permission you can only work up to 28 hours per week.

If you work beyond the scope of your permission, you may not be able to extend your period of stay next time.