According to one embodiment of the present invention, it is possible to realize a signal transmitter which is capable of reducing power consumption and which can be easily designed. A differential transmitter block outputs differential output signals fixed to a predetermined logic signal to a differential receiver block and disconnects terminating resistors from a signal transmission path in an idle state. In the differential receiver block, a differential comparator outputs a logic determined by symbols of the differential output signal from the differential transmitter block, and an operating state detector detects the idle state upon detection that time successively outputting a predetermined logic by the differential comparator reaches a predetermined time, and controls switches so as to disconnect the terminating resistors from the signal transmitter in the receiving side upon detection of the idle state.