Everyone under the "Student (留学)" status of residence has been permitted to stay in Japan under the premise that they will get an education at a university. For that reason, to engage in a part-time job, an activity not permitted under the "Student (留学)" status of residence, you are required to obtain "Permission to Engage in an Activity Other Than That Permitted under the Status of Residence Previously Granted" at the immigration bureau before engaging in said activity.