PURPOSE: To execute optical computation with simple constitution by multiplying 2 sets of light signals inputted in bit parallel by mixed-binary values, then converting the same to binary values.

CONSTITUTION: Light guides 12-0-1, etc., corresponding to the bits of multipliers 13-0W13-2 are respectively provided to bit inputs 12-0W12-2 of multiplicands. Optical switches 14 are provided to the guides 12-0-1, etc., to meet the inputs of the multipliers 13-0, etc. The multiplied values are thereby guided as the mixed-binary (MB) values to light guide parts 15-0, etc. Light guides 51, binary value converters 52 of the MB values and light guides 53 for carry are thereafter provided as shown in the figure. The converters 52 output the signal of the unit quantity of light and the quantity subtracting the unit quantity of light from the input and dividing the result thereof by 2 if the inputs are odd times the unit quantity of light. The converters output only the signals of the quantity half the inputs if the inputs are even times the unit quantity of light. As a result, d0Wd5 are obtd. as bit parallel outputs in an output terminal 16.