A frame plate (19) is mounted to the inside of a case (4) of a magnetic recording device (1), and a disk drive motor and a head body (5) are mounted to the frame plate (19). A member (88) for preventing the deformation of the case is provided between the case (4) and the frame plate (19). The member (88) is placed in a cartridge passing area by the action of a spring in the absence of the cartridge (2), but the member (88) is pressed with the front end of the cartridge (2) when the cartridge (2) is moved forward, the member (88) is forced to retreat to the outside of the cartridge passing area.