An encoder includes a scale having graduations arranged in a measurement direction, a head including a light receiving unit configured to receive, via the scale, light emitted from a light source, and being configured to detect a relative movement amount with respect to the scale by relatively moving in the measurement direction of the scale, and a control unit configured to control the head. The control unit includes a light amount control unit configured to perform control so as to keep a predetermined light receiving amount by increasing or decreasing a light amount of the light source, an error determination unit configured to determine an error based on light received by the light receiving unit, and a light amount suppression unit configured to suppress a light amount of the light source by stopping control performed by the light amount control unit, when the error determination unit determines as an error.