A write sensitive width is calculated by writing a test data by a write head by moving the write head in a radial direction of a magnetic recording medium at a designated speed K to obliquely cross a designated track or a track adjacent to the designated track, reading the test data recorded in the track obliquely by a read head to obtain a read characteristics profile of a read voltage with respect to the track scanning time and obtaining a moving distance in the radial direction of the head by multiplying the test data scanning time of the read head with the designated moving speed K.