A magnetic encoder device (3) of the present invention includes a base portion (33) having a mounting surface (33b) for mounting to a rotary shaft (2), a cored bar (35) fitted and fixed over the base portion (33), and a double-row magnetic encoder track (30) formed on the cored bar (35). Through movement of each of magnetic poles of the magnetic encoder track (30) over a region opposed to a magnetic sensor (4), an angle of the rotating rotary shaft is detected. The base portion (33) is formed of a sintered metal, and the mounting surface (33b) is subjected to sizing.