An arithmetic unit capable of reconfiguring circuitry in accordance with configuration data supplied includes a data processing unit performing a processing using input data; an output data maintenance unit maintaining the result of the processing to output it as an output data; and an output valid signal control unit outputting an output valid signal indicating whether or not the output data is valid, in which an output timing of a valid data to outside the arithmetic unit can be controlled optionally by controlling the output timing of the output valid signal.