PURPOSE: To obtain a high-accuracy approximate function, by increasing the number of relational amplifiers for a broken line approximate function generator for control of an analog switch that sets the gain of an operational amplifier by a relational amplifier.

CONSTITUTION: The values from small Ei1 to large Ein are set previously to the setters 6-1W6-N. When the input Ei becomes equal to either value of the setters 6-1W6-N, the corresponding relational amplifiers 1-1W1-N deliver the outputs V1W Vn to turn on the corresponding analog switches 3-0W3-N and then switch the corresponding gain setting volumes 7-0W7-N of operational amplifier 4. If the negative feedback ratio of amplifier 4 is set at (k), the output Eo is set as Eo= (R2/R1).(1/k)Ei. When the volume is set at is limit, k=1 is obtained. Accordingly the ratio (k) varies every time the input Ei becomes equal to the set value of setters 6-1W6-N. Thus the slope of the broken line varies for the output Eo. In this connection, the accuracy of approximate function can be increased higher as the number of comparators 1-1W1-N increases.