PURPOSE: To avoid locking a diskette at a wrong position by providing a lifter cam which allows a collet hub to be locked by a spindle and keeping the position control of the diskette until the collet hub is connected to a spindle.

CONSTITUTION: A clamp lever 4 is attached rotatably to a lifter hub 6 and at the same time a lifter cam 3 is held rotatably to the hub 6 and allows a collet hub 1 to be connected to a spindle 2 when the lever 4 is actuated. Therefore the hub 1 is not connected quickly to the spindle 2 by the lever 4 owing to the presence of the cam 3. Thus the position of a diskette is controlled to the spindle 2 immediately before the hub 1 is connected to the spindle 2. Then the lever 4 is actuated to lock the diskette 5 to the spindle 2. This device prevents locking of the diskette 5 to the spindle 2 at a wrong position and then improves the quality of a flexible disk device.