PURPOSE: To prevent the generation of a pseudo locking state so as to prevent an abnormal operation by providing a protrusion to prevent the pseudo lock at the reverse side of a rotation center of a lock lever.

CONSTITUTION: The protrusion 11 is provided at the reverse side of the rotation center of the lock lever 4. When a cassette holder moves to the loading state, a pin 2 mounted on the holder is brought into contact with the lock lever 4. However, the protrusion 11 is moved in the direction E since the protrusion 11 is formed on the lock lever 4, and a force is applied in the direction to push back the holder and the lock lever 4 is not pushed in the direction D, therefore, a lock pawl 3 is not released. Thus, the pseudo lock which is detected as being loaded though the holder is not loaded due to vibration, etc., is prevented. After that, the pin 2 is normally moved in the direction D to push the lever 4, then the pin 2 is locked by a spring 5 after the lock pawl 3 is released.