ENCODER, SERVO MOTOR, SERVO SYSTEM, AND ENCODER CONTROL METHOD

An encoder includes: an optical module that detects angular position information indicating an angular position of a rotating disk within one rotation thereof; a magnetic detecting unit that detects multi-rotation information indicating the number of rotations of the disk; a battery that supplies a power to the magnetic detecting unit when an external power is not supplied to the encoder; and a connector that connects connection terminals of the battery to a substrate to which at least one of the optical module and the magnetic detecting unit is connected, via solders in contact with the connection terminals.