PURPOSE: To detect write malfunction such as restoration of old copied recording due to off-track at data write by discriminating dissidence between a write gate signal and a write enable signal.

CONSTITUTION: A gate circuit 22 is provided, which sets/resets a write gate signal 4 as a write command inputted from an R/W control LSI 21 and outputs a write enable signal 6 to sets/resets a write current given to an R/W head 26 via the write enable signal. Then the dissidence between the write gate signal and the write enable signal is discriminated via a WG dissidence detection gate 25 and a control CPU 24 to detect a write malfunction. Thus, a data part stopping the actual write onto a magnetic disk in the output of the write gate signal through the detection of the signal dissidence is specified and the data not written is correctly written later. Thus, unexpected processing of copied recording being readout of older data is prevented.