A disk controller IC (11), driven by a first supply voltage (V1), is provided with a push-pull type output circuit having an output terminal (P1). The output circuit may be turned ON/OFF by a control signal. On the other hand, disk driver IC (12) is provided with a first voltage and a series of a pull-up resistor (R1) and a diode (D3) connected in series between an input terminal and the first supply voltage. An interface is established for the ICs (11, 12) by connecting the output terminal (P1) and the input terminal (P2) together.