To provide a briefcase which enables work and transmission of record even outside an office.

Inside an upper lid of an aluminum briefcase, a personal computer, word processor, or the like is fixed by installing a U-shaped rail on the right and left sides, holding the personal computer or the like between the rails to be slid, and adjusting the width. Further, the personal computer or the like is fixedly held down with an inner lid to be prevented from being damaged.