In a level shift circuit according to the invention, either an input signal IN or an inverted input signal XIN, which are input into the gate electrodes of n-type transistors 1, 2 for signal input, is also given to the substrate of that n-type transistor via p-type transistors 5, 6 for substrate bias. When the signal IN or XIN rises and changes, the threshold voltages of the n-type transistors 1, 2 for signal input is lowered due to the substrate bias effect. Consequently, even if the signal IN or XIN has a low voltage level, operation is carried out at high speeds. Also, when either an output signal OUT or an inverted output signal XOUT is changed to a high voltage level, the transistors 5, 6 for substrate bias become non-conducting, and thus the input signal IN or the inverted input signal XIN is not supplied to the substrate of the n-type transistors 1, 2 for signal input other than when the signal is changing. Consequently, a constant passing-through current does not flow to the substrate of these transistors.