First to fourth magnetic detection units (22-25) are arranged in opposition to a multipole magnetized surface (21a) of a multipole magnet (21) of a magnetic encoder (17). The first and second magnetic detection units (22, 23) are placed on positions separated from each other by 180 degrees on the periphery of the center of the multipole magnet and output an A-phase signal and a B-phase signal. The third and fourth magnetic detection units (24, 25) are placed on positions separated from each other by nearly 180 degrees on the periphery of the center of the multipole magnet and output an A-phase reverse signal and a B-phase reverse signal. Detection signals of the same phase are synthesized and averaged, and consequently a detection error generated by an outer magnetic flux extending in the diameter direction of the multipole magnet can be removed. The signal obtained by synthesizing the detection signals of the same phase and averaging the same and the reverse signal of a signal obtained by synthesizing reverse signals of the reverse phase and averaging the same are synthesized and averaged, and consequently the detection error generated by the outer magnetic flux radially extending in one direction along the radius direction of the multipole magnet can be removed.