PURPOSE: To easily and manually demagnetize the magnetic tape in a cassette by continuously winding electromagnetic coils around two iron core sections in the same direction so that a large AC magnetic field can be generated through a void between two heads facing each other.

CONSTITUTION: When an alternating circuit of 50Hz or 60Hz is made to flow to a serial circuit composed of two electromagnetic coils 1A and 1B and two thermal. switches 3A and 3B by closing a power switch 5, an AC magnetic field MF which has a prescribed intensity at the central part of a void 6 between two heads 2A and 2B facing each other and passes through the void 6 is obtained. After turning on the switch 5 and generating the magnetic field MF, a cassette housing a wound video tape is inserted into the void 6 between the heads 2A and 2B from one end of the cassette while the other end of the cassette is held by hand and the video tape is manually made to slowly come out of or get in the void 6 between the heads 2A and 2B. Then the video tape is extracted and separated from the device by a prescribed distance. After separating the tape, the power switch 5 is turned off.