PURPOSE: To improve the breakdown withstanding voltage of an input protective resistor, or to shorten the retardation time of an input section by constituting an input protective circuit by using a punch-through transistor, which can clamp input applied voltage at voltage higher than a diode for a conventional circuit, and splitting voltage applied to the input protective resistor by the transistor.

CONSTITUTION: Punch-through transistors 9, 10 connected in series between maximum potential 2 and minimum potential 3 can clamp input applied voltage at voltage higher than a conventional input protective diode. A junction C between both transistors 9, 10 is connected to a gate 13 in insulated gate field- effect type semiconductor elements 11, 12. Both semiconductor elements 11, 12 are each shaped in P channel and N channel insulated gate field-effect type semiconductor elements, and a terminal 14 represents outputs from both semiconductor elements 11, 12. Input voltage is applied to one end of an input protective resistor 18 consisting of polycrystalline silicon positioned on an insulator, and the other end is connected to the junction C.