PURPOSE: To protect integrated circuits on a printed circuit board from an electrostatic noise by short-circuiting signal pins of an interface connector and corresponding grand pins.

CONSTITUTION: When the magnetic disk device 20 is received/shipped, a freely attachable/detachable short plug 27 is mounted on the interface connector 22 to short-circuit the signal pin 22A and the grand pin 22B. By this arrangement, a current caused by the noise does not flow into a CMOSIC even if the electrostatic noise is impressed on the device 20, therefore, the integrated circuits are prevented from the destruction due to an overcurrent. Also, the whole signal pins may be short-circuited by plural lead wires without short-circuiting the signal pins and grand pins individually.