PURPOSE: To obtain an arithmetic unit which does not use any digital arithmetic circuit as the arithmetic unit for making arithmetic operations on plural digital signals and outputs obtained results in the form of analog signals.

CONSTITUTION: Constant-current sources 19-26 are connected to switches 11-18 which open and close in accordance with input digital signals. The current sources 19-26 are provided at every input bit and connected so that electric currents can be added at every item of the input bits. The currents added at every item are inputted to a resistance ladder 9 and the ladder 9 outputs output voltages corresponding to the inputted currents.