PURPOSE: To protect cassette from damage in a cassette mount/dismount carrying device, by providing an advance/retract mechanism for reciprocating a device for holding a cassette releasably and performing mount/dismount, carry-in and carry-out of cassette.

CONSTITUTION: A magnetic recording/reproducing device 2 is held on a baseboard 16 to be carried on a conveyor 16 while a cassette conveyor 3 for carrying a cassette 1 onto a conveyor 15 is provided to carry the cassette through advance/retract mechanism 24, air-cylinder 11, cassette holding air-cylinder 13 and rotary motion mechanism 25. Selection of inserting angle of cassette 1 into magnetic recording/reproducing device 2 to be determined by regulation of height through up/down mechanism 26 and inclination of advance/retract mechanism 24 through rotary motion mechanism 25 is facilitated. Consequently, the cassette is protected from damage while changing of installing position is facilitated.