In the Schmitt trigger circuit, a common input signal is supplied to first and second wave-shaping circuits, which have different threshold voltages and which provide different output wave-shaped signals. These wave-shaped signals are alternately selected by a selection circuit to provide the composite Schmitt trigger output signal. When the logic level of the output signal of the selected wave-shaping circuit is inverted due to a change in the input signal to that selected wave-shaping circuit, the output of the other wave-shaping circuit is selected by the selection circuit to provide the Schmitt trigger output signal.