PURPOSE: To obtain a 1/n check circuit which can be expanded to a 1/(n×m) check circuit easily and checks that an output signal is output to one of n output lines.

CONSTITUTION: In a 1/n check circuit of a circuit which transmits an output signal to one of n output lines 4 by decoding an address information by a decoder 3, an address-screening means 5 for outputting an operation signal when it is detected that the address information which is input along with a control signal corresponds to an address of the output line is provided. Furthermore, an 1/n output confirmation means 6 which monitors the output signal and the operation signal, outputs a first potential display signal to a first confirmation display line 7 and a second confirmation display line 8 when no operation signal is output, and then outputs the first potential display signal to the first confirmation display line 7 and a second potential display signal to the second confirmation display line 8 when the operation signal is output and the output signal is output from only one of n output lines is provided.