According to one embodiment, an arithmetic device includes: a first input terminal; a second input terminal; an output terminal; a first logical shifter; a second logical shifter; a third logical shifter; a first AND gate; a second AND gate; a first multiplexer; a third AND gate; a first adder; a fourth logical shifter; a second multiplexer; a second adder; a first arithmetic shifter; a second arithmetic shifter; a third arithmetic shifter; a third multiplexer; a fourth multiplexer; and a fifth multiplexer.