An optical encoder includes an origin point detection scale having an origin point detection pattern and an inverse origin point detection pattern that is the inverse of the origin point detection pattern; a light source emitting light at the origin point detection scale; a light source grid that is inserted on the light source side of the origin point detection scale, the light source grid having two first light source grid patterns corresponding to the origin point detection pattern and the inverse origin point detection pattern, respectively; a photoreceiver detecting a signal from light that has passed through the origin point detection scale; and a photoreceiver grid inserted on the photoreceiver side of the origin point detection scale, the photoreceiver grid having two first photoreceiver grid patterns that are a pattern either identical to or the inverse of the first light source grid pattern.