An abnormality detection method of an encoder for detecting an abnormality of the encoder by using a robot control unit, the encoder detecting a rotational position of a motor that drives an output shaft of an operation device, the robot control unit including a controller which outputs a speed command and command position information, the speed command being a command for instructing the rotational position of the motor, and the command position information indicating the rotational position of the motor calculated from the speed command, a driver connected to the encoder and the controller, and an abnormality detection device connected to the encoder and the controller, the method comprising: an output step of outputting the speed command and the command position information; a control step of receiving the speed command and an output signal having a rotational position of the motor detected by the encoder, and controlling driving of the motor based on the speed command and the output signal; an information acquisition step of acquiring the command position information from the controller, and acquiring the output signal from the encoder; and an abnormality determination step of comparing the command position information from the controller with detection position information on a current position of the motor calculated based on the output signal, and determining that the encoder is abnormal in a case where a difference between the command position information and the detection position information of the motor is equal to or more than a predetermined value. the robot control unit including a controller which outputs a speed command and command position information, the speed command being a command for instructing the rotational position of the motor, and the command position information indicating the rotational position of the motor calculated from the speed command, a driver connected to the encoder and the controller, and an abnormality detection device connected to the encoder and the controller, a controller which outputs a speed command and command position information, the speed command being a command for instructing the rotational position of the motor, and the command position information indicating the rotational position of the motor calculated from the speed command, a driver connected to the encoder and the controller, and an abnormality detection device connected to the encoder and the controller, the method comprising: an output step of outputting the speed command and the command position information; a control step of receiving the speed command and an output signal having a rotational position of the motor detected by the encoder, and controlling driving of the motor based on the speed command and the output signal; an information acquisition step of acquiring the command position information from the controller, and acquiring the output signal from the encoder; and an abnormality determination step of comparing the command position information from the controller with detection position information on a current position of the motor calculated based on the output signal, and determining that the encoder is abnormal in a case where a difference between the command position information and the detection position information of the motor is equal to or more than a predetermined value. an output step of outputting the speed command and the command position information; a control step of receiving the speed command and an output signal having a rotational position of the motor detected by the encoder, and controlling driving of the motor based on the speed command and the output signal; an information acquisition step of acquiring the command position information from the controller, and acquiring the output signal from the encoder; and an abnormality determination step of comparing the command position information from the controller with detection position information on a current position of the motor calculated based on the output signal, and determining that the encoder is abnormal in a case where a difference between the command position information and the detection position information of the motor is equal to or more than a predetermined value.