PURPOSE: To simplify the constitution of an input circuit and also to prevent the noise having the short pulse width and a high voltage level, by preventing the input of short pulse width with increase of the threshold voltage level and keeping a normal threshold voltage level with the input of the long pulse width.

CONSTITUTION: An input circuit consists of an n channel MOSFET which contains an input terminal 11, an output terminal 12, enhancement type transistors 14∼16 having the same threshold voltage level and the same substrate potential, a depression type TR17 serving as a load TR, a resistance 18 which performs the integration of output signals, and a capacitor 19. Furthermore the power supply terminals 13 and the earth terminals 1G are added. The TR15 conducts when the voltage higher than VT is impressed to the terminal 11. Thus the potential at a point B is approximately equal to the earth potential and therefore the TR14 conducts. Then the terminal 12 delivers logic 'O' to turn off the TR16.