To provide a semiconductor device suitable for a low-amplitude LVDS, and a signal transmission system.

A first current source MOSFET is provided on the side of a first operation voltage. The current of the first current source MOSFET is made to flow into one of a pair of output terminals by switching it corresponding to an input signal with a paired first differential MOSFET. A second current source MOSFET is provided on the side of a second operation voltage. A current of the second current source MOSFET is made to flow into the other of a pair of the output terminals by switching it corresponding to the input signal with a paired second differential MOSFET. Either one level of a high level and a low level of output voltages which are outputted from a pair of the output terminals and respectively extracted via a first or second switch element corresponding to the input signal, is compared with a first reference voltage by a first differential amplifier circuit, so that a gate voltage of the first current source is controlled by the first differential amplifier circuit, in order to make the either one level of a high level and a low level of the output voltages and the first reference voltage coincident with each other. A gate voltage of the second current source MOSFET is controlled by a second differential amplifier circuit, so as to make each midpoint voltage of the output voltages outputted from a pair of the output terminals and a second reference voltage coincident with each other.