PURPOSE: To increase the lifetime of a driving system and at the same time to reduce the power consumption by detecting the shift of a clamp lever containing a clamping mechanism which revolves a magnetic medium and therefore giving a driving command to a spindle drive system.

CONSTITUTION: A clamp lever 5 is shifted toward an arrow after a diskette 1 is inserted along a guide 2 as shown by dotted lines, and a sensor 9 detects instantaneously the shift of the lever 5. Therefore a switch 101 is turned on through a switch control circuit 10, and a motor 6 starts its revolution. At the same time, a spindle 3 is also turned. Then a clamping mechanism 4 moves to oppose to the spindle 3. Thus the spindle 3 is revolved and at the same time set opposite to the diskette 1. This facilitate easy positioning of the spindle 3. At the same time, the spindle 3 is revolved only when the lever 5 operates. This can reduce the power consumption of a spindle drive motor and also increases the lifetime of the spindle drive system.