To measure the durability of a magnetic tape easily and quantitatively by sliding the magnetic tape to be inspected onto a sliding face of a magnetic head and then photographing a tape sliding face of the magnetic head.

A magnetic tape to be inspected is slid on a tape sliding face of a plurality of magnetic heads of a rotary drum 7. Thereafter the tape sliding face of each magnetic head is enlarged by a microscope 5 and photographed by a CCD camera 6. Among pixels constituting an image, a ratio of the pixels wherein powder attaching to the magnetic head due to powder dropping from the tape is photographed is obtained as powder drop on a sliding face. In addition, regions other than the tape sliding face of each magnetic head are photographed, and a ratio of pixels wherein powder attaching to the magnetic head due to dropping has been photographed is obtained as a powder drop ratio on a non-sliding face. The based on the powder drop ratio on the sliding face on the magnetic head with the largest powder drop ratio on the sliding face and an average of powder drop rations on the non-sliding face of all magnetic heads, whether the magnetic is good is determined.