PURPOSE: To execute simple parallel optical computation from mixed-binary values to binary values by means of an optical converter which outputs light signals of different quantities according to whether the light signals of parallel inputs are odd times or even times the unit quantity of light.

CONSTITUTION: The parallel mixed-binary (MB) inputs X0WX4 are converted to the binary (B) values d0Wd5 by the following constitution: Light guides 12 connected to an input terminal 11, optical converters 3 for one digit for converting MB to B, light guides 14 for carry light signal and light guides 15 for the light signals after conversion are provided as shown in the figure. The converters 13 output the 1st signal corresponding to the unit light quantity for the input of the odd times the unit quantity among the inputs X0WX5 and the 2nd signal corresponding to the input of half the quantity subtracting the unit quantity from the inputs at this time. The converters output only the 2nd signal of the quantity of the light corresponding to half the inputs for the inputs of even times the unit quantity among the inputs X0WX5. As a result, the parallel computation from n+m-1 pieces of the MB values to n+m bits of the B values is easily executed.