An interface circuit includes first and second MOS transistors of depletion type, first and second switching elements, and a control circuit. The current path of the first MOS transistor is connected between an output node of a MOS circuit formed in a semiconductor substrate and an output terminal and the gate thereof is connected to a power supply. The first switching element is connected between the backgate of the first MOS transistor and a ground terminal. The second switching element and the current path of the second MOS transistor are serially connected between the backgate of the first MOS transistor and the output terminal. The gate of the second MOS transistor is connected to the power supply and the backgate thereof is connected to the backgate of the first MOS transistor. The first and second switching elements are set into complementary states according to an output of the MOS circuit in response to an output signal of the control circuit.