PURPOSE: To obtain an accurate gap and to prevent damage on a surface of a head by moving vertically a magnetic head and adjusting a gap confirming an indicated value of a gap.

CONSTITUTION: After a head unit is mounted to a an adjusting device 14 of a unit frame of a head unit so as to be clamped, centering of a roller is performed by a centering block to decide the center position of the roller. And a magnetic head is mounted to the unit frame, and tilt of the roller for the magnetic head is displayed on a CRT display through a picture discriminating device 18 receiving the light from an illuminator 16 with a CCD camera 12. Adjustment is performed observing this gap displayed by a picture.