Patent ID: 8044340

Claim:
An encoder comprising: a rotating member; a light source device for emitting light to be detected to the rotating member; and a photodetecting device including a scale having a plurality of photodetecting elements arranged thereon, and an output portion for outputting an output signal based on light intensity of the light to be detected made incident to the photodetecting elements through the rotating member, wherein the photodetecting elements are arranged along an annularly arranged line on the scale, and the rotating member is designed so that, in the scale, an area containing mutually separate parts of the arranged line is set as a bright portion to which the light to be detected is irradiated, and an area containing the other portion excluding the parts of the arranged line concerned is set as a dark portion to which no light to be detected is irradiated, wherein the light to be detected is irradiated at, at least, two mutually separated spots of the arranged line.