PURPOSE: To prevent the writing malfunction at the time of the interruption of a power source by providing a writing malfunction preventing circuit in parallel between a driving circuit and a head driving control circuit.

CONSTITUTION: The writing malfunction preventing circuit 3 does not operate as the transistor Tr 1 thereof is off in the normal time when the power source of the device is not interrupted. A writing action is executed without a response delay by the input of a writing control signal -WS to the head driving control circuit when this writing control signal is outputted from the driving circuit 1. The transistor Tr 1 turns on and the writing malfunction preventing circuit 3 operates to pass a current via a capacitor C 1 and the Tr 1 to the driving circuit 1 when the power source of the device is interrupted; therefore, the operation of a head driving controller 2 is prevented. The writing by the malfunction of the driving circuit at the time of the interruption of the power source is, therefore, surely prevented.