PURPOSE: To provide the logic circuit, which can more reduce circuit scale and can more shorten an operation processing time, concerning the logic circuit for simultaneously adding four pieces of one-bit data.

CONSTITUTION: This logic circuit simultaneously adds the four pieces of one-bit data (a), (b), (c) and (d) and is provided with a sum output circuit 1 for calculating a sum S of the four pieces of one-bit data (a), (b), (c) and (d), one-bit carry circuit 3 for generating a 1st digit carry output Ca at the time of adding the four pieces of one-bit data (a), (b), (c) and (d), and two-bit carry circuit 5 for generating a 2nd digit carry output Cb at the time of adding the four piece of one-bit data (a), (b), (c) and (d).