RECORDING AND REPRODUCING DEVICE

PROBLEM TO BE SOLVED: To reduce the restriction as to a recording medium cartridge by preventing the erroneous insertion of the recording medium cartridge. SOLUTION: The recording/reproducing device is constituted in such a manner that a recording medium disk is housed in the nearly rectangular cartridge 410 and a groove 414 is formed on the end surface along one side of the rectangle of the cartridge 400, and a disk tray 250 for mounting the recording medium disk to the prescribed mounting position is provided, and thereon, a working piece 293 relatively moving by being inserted to the groove when the disk cartridge 400 is inserted facing in the proper direction, a disk slider having a disk pressurizing piece 263 for abutting on the end part of the inserting side while being freely movable to the inserting direction, and a lock means 282 to the interrupting position where the slider is abutted by the disk pressurizing piece 263 on the end part of the inserting side of the disk cartridge 400 at the intermediate position uninserted to the prescribed position for the disk cartridge, are furnished.