A fitting mechanism includes a door member that is provided on a front side of a housing area for accommodating a terminal device and opens and closes the housing area, and a supporting member that is provided on a back side of the housing area and supports the terminal device accommodated in the housing area by urging the terminal device against the door member. The supporting member is urged toward the front side and has an abutting portion that abuts against the terminal device, the abutting portion being movable in a depth direction of the housing area within a predetermined movable range.