PURPOSE: To attain the change of a program easily by supplying electric signal having a predetermined level from an analog signal generating circuit to an analog/digital conversion circuit so as to obtain a desired digital output signal.

CONSTITUTION: The analog signal from the analog signal generating circuit 3 is given to the analog/digital conversion circuit 1, from which a digital output signal is obtained. The electric signal generated from an analog signal generating circuit 2 is an electric signal having a predetermined level to obtain a desired digital output signal from the analog/digital conversion circuit 1. Thus, the level of the electric signal led from the analog signal generating circuit 2 and fed to the analog/digital conversion circuit 1 is changed to obtain a desired digital output signal from the circuit 1. It is easily possible for the analog signal generating circuit 2 to combine, for example, a resistor and a switch to generate an electric signal having a predetermined level.