PURPOSE: To correctly set a multiplying factor with two inexpensive components by combining an operational amplifier and a multiplication type D/A converter.

CONSTITUTION: The scanning signal input is inputted to the nonreverse input terminal of an operational amplifier 1. The output of the amplifier 1 is inputted to the analog input terminal of a multiplication type D/A converter 2, and it is outputted as the scanning signal input to the outside. The output of the converter 2 is applied to the reverse input terminal of the amplifier 1. The multiplying factor control signal is inputted to the digital input terminal DIN of the converter 2. The output voltage Vo of a multiplying factor control circuit is indicated by the equation I, where Vin is the input voltage and Din is the multiplying factor control signal value, and the output voltage and the multiplying factor control signal are inversely proportional to each other. When the multiplying factor is controlled up to 1-10 times with the increment of one in this circuit, the multiplying factor can be correctly set by the 4-bit converter 2. The multiplying factor can be correctly set by the inexpensive amplifier 1 and converter 2.