Abstract: The magnetoresistive detector of the present invention uses magnetoresistive elements for detecting changes in the magnetic field of a moving magnet 3 which changes a magnetic field, wherein bias magnets (21, 22, 23, 24) can be mounted without using positioning jigs, errors in mounting are prevented, and the mounting density of components on a printed circuit board (4) is improved, whereby improved quality and compactness of the magnetoresistive detector can be achieved. For that purpose, the shape and dimensions of magnetoresistive detector elements (11, 12, 13, 14) are made identical to the shape and dimensions of the bias magnets (21, 22, 23, 24), and on the printed circuit board (4), positioning sections (41) for simultaneously positioning the magnetoresistive detector elements (11, 12, 13, 14) and bias magnets (21, 22, 23, 24) are provided.

Abstract: An optical encoder that accurately performs rotation while protecting a rotating disk from dust. The optical encoder comprises a shaft (5) supported by a bearing (6) in a housing (1), a rotating disk (8) fixed to the shaft (5), a light-emitting element (10) mounted on the housing (1), a photodetector element (12) mounted on a sub-board supported by the housing (1) for receiving the light passing through or reflected by the rotating disk (8), and a main substrate (13) mounted on the housing and provided with a circuit for determining the quantity of rotation or the angular position form the light received by the photodetector element (12). The housing (1) includes a holder (9), which as an annular cover (9a) engaged with the border of the main substrate (13) and a retainer (9b) formed on the cover (9a) for holding the light-emitting element.