To provide a method and a device which reduce common-mode radiation noise energy without attenuating a communication line signal level in normal mode.

This device is characterized by that the earth of an LSI is connected to a housing through a substrate, a connector, and a back board boss and the communication line from an output terminal is led out of a front panel. Then one 1st common-mode choke coil is inserted between a 1st output pin of the LSI and a 1st signal line and one 2nd common-mode choke coil is inserted between a 2nd output pin and a 2nd signal line; and a load is connected between the 1st and 2nd signal lines and the other 1st and common-mode choke coils are inserted between an artificial grounding surface of the housing and the earth terminal of the LSI. Consequently, common-mode radiation noise generated between the earth of a semiconductor integrated circuit device and the housing as a main radiation noise source on signal lines is removed without exerting any influence on a normal-mode signal.