PURPOSE: To protect a floppy disk driving device and information on floppy media by providing a means which measures the rotating speed of a main spindle motor and detecting the abnormal rotation of the main spindle motor, and stopping the main spindle motor and sending a warning, etc., out.

CONSTITUTION: A part encircled with a broken line in figure is in the floppy disk driving device and 101 is a floppy disk control circuit outside of the device. When the control circuit 101 sends a main spindle motor rotation signal 105 to a means 102 which judges whether the rotation of the main spindle motor is normal or not, the means 102 sends a main spindle motor rotation signal 106 to the main spindle motor 104, which rotates the main spindle motor. The measuring means 103 for measuring the rotating speed of the main spindle motor measures the rotating speed of the main spindle motor 104 and transmits rotating speed information 108 to the means 102. The means 102 judges whether the rotation is normal or not on the basis of the rotating speed information 108 to send an information writable signal 107 to the floppy disk control circuit when the rotation is normal or stop the main spindle motor rotation signal 106 when not.