PURPOSE: To simplify the mechanism and to constitute it out of a small number of parts and to drastically reduce the cost by performing two operations of a disk loading operation and a chucking operation with one cam member.

CONSTITUTION: When a cam plate body 30 is operated to move backward (in the direction of an arrow (c)), a vertical edge part 33d of a cam groove hole 33 is brought into contact with a supporting pin 4 of a tray 2 to come under the state of pressing this, and the tray 2 is lowered, and a turntable 8 is entered into a disk cartridge 1 via an opening 2b, and a disk D is mounted on the turntable 8, thus completing the disk loading operation. At the same time, a chucking plate 9 is also lowered, and by moving the cam plate body 30 backward, the inclined edge part 40a of a cam piece 40 is brought into contact with a roller 28 and continuously presses it, thus performing a lowering operation of the chucking plate 9. Then, the chucking plate is inserted in the disk cartridge 1 to hold the disk D in pressurized clamped, state thus completing the disk chucking. By this method, the number of parts is reduced and an inexpensive disk loader can be obtained.