An optical encoder 10 comprising: a light source 11; a splitter 12 splits a light from the light source 11, a light receiving unit 16; a scale 13 is arranged on a light path and movable in a measurement direction, a grating being arranged on a main surface of the scale; and an offset diffraction grating 14 includes a plurality of diffraction gratings arranged in the optical path from the splitter 12 to the light receiving unit 16, the plurality of diffraction gratings diffracting the split lights with different phases, wherein, the plurality of diffraction gratings 13 in the offset diffraction grating 14 are arranged in one plane parallel to the main surface of the scale and are offset each other in an offset direction orthogonal to the measurement direction, the light receiving unit 16 includes a plurality of light-receiving elements 16-11 to 16-23 arranged in the offset direction.