PURPOSE: To detect that a recording medium is brought into contact with and is slided on a magnetic head, by detecting the reflection state of a laser beam from the surface of the recording medium.

CONSTITUTION: The laser beam which is reflected on a magnetic disc 10 and is returned to a laser 7 is stabilized in the normal operation state and has only a gentle change due to rotation of the magnetic disc. However, if a slider 5 is brought into contact with and is slided on a magnetic disc 10, the change of a high voltage is generated in a laser terminal voltage, and this change is taken out by a filter 12 and is amplified by an amplifying circuit 13 and it applied to a detecting circuit 14. When the output of the amplifier exceeds a reference value, the detecting circuit 14 discriminates the occurrence of slide to send the detection signal to a control circuit, and the control circuit stops the magentic disc and transmits an abnormality indication signal to a computer body or the like to which the magnetic head is connected. Thus, troubles due to slide are held down to a minimum.