A reliable encoder capable of reducing vibration of a printed board when the encoder is subjected to vibration or shock, by means of a simple structure. The encoder has a housing, a rotating code plate arranged in the housing and configured to rotate in synchronization with an object to be measured, a printed board attached to the housing and positioned above the rotating code plate, wherein the encoder has a reinforcing member configured to contact a portion of the printed board where the displacement of the printed board is large while the printed board is resonated due to vibration or shock applied to the encoder.