PURPOSE: To obtain a simple and compact loading mechanism excellent in vibration proof and operability in a tray type optical disk cartridge loading device.

CONSTITUTION: A lock engaging part 6j, a damper 7, etc., are mounted on a frame unit 6 which is used as the base of a disk recording/reproducing device. Next, a chassis unit 5 including a driving motor 18 and a magnetic head 20 is floated through the damper 7. Further, an inside tray unit 4 is mounted on a guide unit 3 through a cam groove freely movably in the sliding direction and vertical direction. When the optical disk is loaded/unloaded, 1st and 2nd lock levers 12, 14 are engaged with the lock engaging part 6j to pull out the inside tray unit 4. When the optical disk is recorded/reproduced, the lock with the lock engaging part 6j is disengaged, then the chassis unit 5 becomes the high damping state.