PURPOSE: To decrease the capacity of a ROM and to quicken operating speed by providing a conversion table converting a phase angle in a range of a reference phase angle into an amplitude within a reference amplitude range corresponding to the phase angle.

CONSTITUTION: A signal separation switching circuit 110, a conversion section 120 and a code correction circuit 130 are provided on the subject circuit. All the phase angles of a phase signal are converted into phase angles in a reference phase angle range being a specific range in all the phase angles, the phase angle/amplitude conversion is implemented with respect to the converted phase angle and the code is corrected by the information of the amplitude code at the conversion of the phase angle with respect to the converted amplitude. Thus, an LUT ROM used for the conversion section 120 is decreased by 2-bit at the input bit width and by 1-bit at the output bit width. Thus, the ROM capacity is reduced and the operating speed is quickened.