PURPOSE: To reduce the electric field of a gate after input of a voltage even when a voltage higher than a normal rating is inputted by a method wherein an input terminal circuit having an n type transistor with the substrate potential fixed to the ground potential is provided.

CONSTITUTION: An input terminal circuit has an n type transistor 2 with the substrate potential fixed to the ground potential, and the transistor 2 is inserted in series between an external terminal 5 and the input terminal circuit. By preparing the substrate potential of the input terminal circuit independently of the substrate potential of other circuits, electric field induced between the gate electrodes 7 of transistors 1 and 2 and a p type well 13 can be relaxed even when an input signal higher than an initial rating is inputted. In short, by fixing the substrate potential of the n type transistor 2 within the input terminal circuit to which a high electric field is applied to the potential of the ground electrode, Vss, it is possible to reduce the electric field.