PURPOSE: To obtain an inspecting method capable of discriminating a defect shape by inspecting the recording/reproduction defect of a magnetic disk medium by a 1st magnetic head and a 2nd magnetic head which differs in recording/ reproducing gap width from the 1st magnetic head.

CONSTITUTION: The magnetic disk medium 1 rotates at a prescribed rotating speed and the magnetic head a2 and magnetic head b3 inspects errors of the medium 1 respectively. The head a2 has the same track width as that of a magnetic head used actually by a magnetic disk device and the head b3, on the other hand, differs in track width from the head a2. Both heads are mounted on an arm 4, which is fixed to a scanning part 5. A recording and reproducing part 6 records inspection data on the medium 1 by applying a prescribed write signal to the head a2 or b3 or processes the read signal of the inspection data reproduced by the head a2 or b3 from the medium 1. Then when an error detection part 7 detects the read signal of the recording/reproducing part 6 as an error, error information is sent to an error comparison part 8 to discriminate the defective shape.