An employment certificate is required for the application of some visas. A document of this nature usually is valid for 3 months after its issuance. However, the issue is whether an employment certificate issued in February still is valid in April if the salary is written on it since a salary is often raised as of April. The Immigration Bureau is not interested in the salary of the employee. They need to find out whether the person truly is employed by the company. Hence, the certificate on which the previous salary is written is still valid for visa application.