To prevent the great displacement of a mechanical unit caused by an external force applied during nonoperation while maintaining the good damping effect of the mechanical unit during a recording or reproducing operation, and to prevent the generation of faults such as collision with a peripheral part.

In a constitution where a mechanical unit 2 having a mechanical operation mechanism mounted thereon is float supported in an outer case 1 through an elastic damping member 3, first lock levers 5 and 6 and engaging pins 4 and 4 projected from the outer surface 20 of the mechanical unit 2 to be engaged therewith constitute a locking means for locking the mechanical unit 2 in the outer case 1 to inhibit its movement under the operation of the damping member 3, and unlocking buttons 7 and 8 having the bottom plate 10 of the outer case 1 supported through the inside and the outside and projected inside by the pressing of an outer end according to mounting on a mounting surface to swing the first and second lock levers 5 and 6 constitute an unlocking means for unlocking the mechanical unit 2 during a recording or reproducing operation.