A diagnosis method for diagnosing a state of a motor includes an application step in which a voltage is applied to the motor on the basis of a non-rotating voltage signal that causes a rotation speed of the motor to become 0, and a measurement step in which a current supplied to the motor, to which the voltage has been applied, is measured. The diagnosis method includes a calculation step in which an electrical characteristic of the motor is calculated on the basis of the current of the motor measured by the measurement step, and a determination step in which an abnormality of the motor is determined on the basis of the electrical characteristic of the motor calculated by the calculation step and a parameter related to the non-rotating voltage signal.