Abstract: A magnetic encoder apparatus comprises a permanent magnet 2 fixed to a rotating body 1, a magnetic field detection element 4 which is opposed to the permanent magnet 2 through an air gap and attached to a fixed body 3, and a signal processing circuit to process a signal from the magnetic field detection element 4. The permanent magnet 2 is formed into disk-like, and magnetized in one direction which is perpendicular to the shaft of the rotating body 1. The magnetic field detection element 4 is arranged on the outer peripheral side of the permanent magnet 2 through an air gap. Further, the fixed body 3 is formed by a ring-like magnetic substance, and an air gap is provided in the circumferential direction, and the magnetic field detection element may be provided in the air gap portion. Accordingly, a magnetic encoder apparatus in which the structure is simple, the resolution is very high, the accuracy is high, and the size is small, can be obtained.