PURPOSE: To enable a sufficient functional test without increasing the number of testing terminals, by connecting the anode of a semiconductive element, of which the cathode is connected to the input terminal of a logical circuit, not only to the other logical circuit but also to first and second voltage sources.

CONSTITUTION: The cathode of a semiconductive element D1 is connected to the input terminal In of the logical circuit 2 among a plurality of logical circuits 2, 3 and the anode thereof is connected not only to the clear terminals CR of toggle circuits Ta1WTal constituting the circuit 3 being a frequency dividing circuit but also to the ground GND through a resistor R1 and to a voltage source VCC through semiconductive elements D2, D3 connected in reverse directions to each other. Initial setting is applied to the output states of the circuits Ta1WTan by the signal from the input terminal In to perform the functional test of the circuit 3 and, after the test was completed, a current for destructing the junction of the elements D2, D3 is flowed to the power source VCC from the terminal In, and a point (a) and the terminal In are separated to use the terminal In for an original purpose.