An encoder characterized by comprising: a track (SA1, SA2) having optical effecters which are arranged to have an absolute pattern along a measurement direction (c) and configured to reflect or transmit light; a point light source configured to emit diffusion light to the track (SA1, SA2); a light receiving array (PA1, PA2) having light receiving elements arranged along the measurement direction (c), and configured to receive light reflected or transmitted at the track (SA1, SA2), the light receiving elements capable of falling within an area which is positioned corresponding to an area between the optical effecters and to which light reflected or transmitted at the track (SA1, SA2) does not reach; wherein a width (φ) of an emitting surface of the point light source in the measurement direction (c) and a width (x) of the light receiving elements in the measurement direction (c) are set, so that the light receiving elements are capable to fall within the area which is positioned corresponding to the area between the optical effecters and to which light reflected or transmitted at the track (SA1, SA2) does not reach; wherein when the width (φ) of the emitting surface of the point light source in the measurement direction (c) is φ, a minimum width (y) of the optical effecters in the measurement direction (c) is y, a width (x) of the light receiving elements in the measurement direction (c) is x, a distance (u) from the emitting surface to the optical effecteurs is u, and a distance (v) from the optical effecters to the light receiving elements is v, the following relation is satisfied: φ ≤ y × u + v − u × x / v a track (SA1, SA2) having optical effecters which are arranged to have an absolute pattern along a measurement direction (c) and configured to reflect or transmit light; a point light source configured to emit diffusion light to the track (SA1, SA2); a light receiving array (PA1, PA2) having light receiving elements arranged along the measurement direction (c), and configured to receive light reflected or transmitted at the track (SA1, SA2), the light receiving elements capable of falling within an area which is positioned corresponding to an area between the optical effecters and to which light reflected or transmitted at the track (SA1, SA2) does not reach; wherein a width (φ) of an emitting surface of the point light source in the measurement direction (c) and a width (x) of the light receiving elements in the measurement direction (c) are set, so that the light receiving elements are capable to fall within the area which is positioned corresponding to the area between the optical effecters and to which light reflected or transmitted at the track (SA1, SA2) does not reach; wherein when the width (φ) of the emitting surface of the point light source in the measurement direction (c) is φ, a minimum width (y) of the optical effecters in the measurement direction (c) is y, a width (x) of the light receiving elements in the measurement direction (c) is x, a distance (u) from the emitting surface to the optical effecteurs is u, and a distance (v) from the optical effecters to the light receiving elements is v, the following relation is satisfied: φ ≤ y × u + v − u × x / v