Though not restricted, when an input signal is a signal corresponding to the GTL circuit, the threshold voltage of the input MOSFETs Q1 and Q2 is set to a low value such as 0.4 V and the reference voltage Vrefin of them is set to a value such as 0.8 V. In the case of this embodiment, level sensing by the reference voltage Vrefin is not performed like the differential amplifier but current sensing