PURPOSE: To improve the safety and reliability of the title device by moving a couple of slide plates of the cassette loader/unloader in opposite directions to each other simultaneously by an interlocking member so as to prevent the slide plates from being slided by a gravity due to shock or the like, thereby preventing malfunction due to shock or the like in advance.

CONSTITUTION: A couple of the slide plates 7, 8 are slided in directions of arrows (a), (b) opposite to each other by a spring 22 before a disk cassette 2 is loaded to the cassette loader/unloader 4 to lift up the cassette holder 6 in the direction of arrow (c). In loading the cassette 2 to the holder 6 from the direction of arrow (a) in this state to operate a trigger mechanism, the interlocking member 18 is driven in the direction of arrow (d) around a fulcrum pin 19 by the spring 22 and interlocking pins 20, 21 slide simultaneously the slide plates 7, 8 in opposite directions. Plural titled guides 9, 10 tiled in opposite directions provided on the slide plates 7, 8 guide a part 11 to be guided at both ends 6a of the holder 6 to move the holder 6 downward in the direction of arrow (c) orthogonally thereto to set the cassette 2 smoothly.