To prevent damage to equipment due to the oblique insertion of a fat cable, a capacitor-connection line having a capacitive circuit element is disposed adjacent to a power supply line of a printed circuit board and connected to a ground of the printed circuit board. When a flat cable is obliquely inserted, the capacitor-connection line which comes into erroneous contact with the power supply line works as high impedance in the case of a direct current, and the current does not flow. Damage generated when a flat cable is obliquely inserted into a connector of a printed circuit board is prevented in this manner.