An arithmetic device allocation design method of the present invention includes the steps of: in the case of allocating an arithmetic operation A to the arithmetic device, comparing an increased circuit area due to a selector to be provided so as to allocate the operation A to an arithmetic device C to which another arithmetic operation B has already been allocated and an increased area due to an arithmetic device D to be created anew to which only the operation A is allocated; when the increased circuit area due to the selector is smaller, allocating the operation A to the device C to which the another operation B has already been allocated while providing the selector; and when the increased circuit area due to the device D is smaller, creating the device D anew so as to allocate the operation A to the device D created anew.