The photoelectric encoder 1 includes a scale 2, and a detection head 3 including a light emitting unit 4, an index 5, and a detection unit 6. The index 5 includes a first index portion 50 consisting of diffraction portions and non-diffraction portions alternately juxtaposed at a predetermined pitch along the longitudinal direction of the scale 2, and a second index portion 51 consisting of diffraction portions and non-diffraction portions alternately juxtaposed at twice the pitch of the first index portion 50. The scale 2 is configured to include a first pattern portion 20 consisting of diffraction portions and non-diffraction portions alternately juxtaposed at a predetermined pitch along the longitudinal direction of the scale 2, and a second pattern portion 21 consisting of diffraction portions and non-diffraction portions arranged in a checkered pattern.