Single-entry visas (including long-term work visas) are issued with a validity of 3 months from the date of issue. It is not possible to extend this validity.
Double-entry visas has a validity of 6 months from the date of issue.
Multiple-entry visas, on the other hand are issued with longer validity typically in the range of 1 to 5 years, depending on the foreigner's nationality, the type of passport he holds and the purpose of his visit.
When an immigration officer at the port of entry completes an examination for landing and grants landing permission to a foreigner, the Single-entry visa on the foreigner's passport immediately becomes invalid (although multiple-entry visas remain valid until the date of their expiration). After that, it is the stamp of landing permission that serves as the legal basis for the foreigner's stay in Japan.