PURPOSE: To input two kinds of clocks to an internal logic by providing an external clock input pad with a circuit for inputting a clock having a period and duty equal to that of an external clock to the internal logic and a circuit for inputting a clock different from said clock to the internal logic.

CONSTITUTION: An external clock (a) includes earth potential 0V and power supply potential values 5V, 10V, and when the external clock (a) is applied to a clock input pad 1, a signal outputted from an internal logic input clock terminal 2 shows the waveform of an internal logic input clock (b). In the clock (b), the potential part more than 5V of the external clock (a) goes 5V and the residual goes 0V. On the other hand, a signal from an internal logic input clock terminal 3 goes the waveform of an internal logic input clock (c). In the clock (c), only the part corresponding to 5V of the external clock (a) goes 5V and parts corresponding to 10V and 0V of the external clock (a) are 0V. Thus, a required clock can be obtained.