An encoder is provided as one capable of accurately detecting an absolute value of an operating angle or the like of a scale plate in a simple configuration.In this encoder, each of light relay portions 4 formed along an operational direction α in the scale plate has a pattern of a one-dimensional array of some of optically transparent potions 5 and optically nontransparent portions 6 different from those of the other light relay portions. This allows the encoder to identify the light relay portion 4 located on a light receiving region 100, based on second light intensity profile data VY(m), using the patterns as codes. In the identification of the light relay portion 4, the light relay portion 4 can be accurately identified with respect to a position of a reference light propagation portion 7 formed for each light relay portion 4 in the scale plate. Furthermore, the encoder is able to calculate a center-of-gravity position of the identified light relay portion 4 relative to a reference position in the light receiving region 100, based on first light intensity profile data VX(n), and to calculate an operating angle of the scale plate from the center-of-gravity position.