Leakage current in a standby mode of a level shifter capable of operating with low voltage is reduced. Provided is a level shifter circuit in which an n-channel silicon transistor and an oxide semiconductor transistor are provide in series between an output signal line and a low potential power supply line. The potential of a gate electrode of the oxide semiconductor transistor is raised to a potential higher than input signal voltage by capacitive coupling, so that on-state current of the oxide semiconductor transistor is increased.