PURPOSE: To make good recording and erasing without causing trouble by making the saturation magnetic flux density of one of a pair of magnetic cores lower than the saturation magnetic flux density of another magnetic core and reversing the direction of rotation of a discoid magnetic recording medium when recording and when erasing.

CONSTITUTION: Out of a pair of magnetic cores 11, 12 that form a gap (g), the saturation magnetic flux density (Bs) of one magnetic core 11 having thickness t1 is made lower than the saturation magnetic flux density of another magnetic core 12 having thickness t2. At the time of recording, a magnetic disk D is rotated in positive direction, for instance, in the direction of arrow mark A in the figure, and at the same time, the signals supplied from a terminal 21 are sent to a magnetic head 10 through a recording/reproducing processing circuit 22 and a change-over switch 23, and recorded in the magnetic disk D. At the time of erasing, the magnetic disk D is rotated in reverse direction, for instance, in the direction of arrow mark B, and at the same time, the AC signals for erasing are supplied from an oscillator 24 to the magnetic head 10 through an amplifier circuit 25 and a change-over switch 23, and the erasing operation is performed.