A motor controller is provided with: an estimated temperature calculating means that calculates an estimated temperature of a motor; and a control unit that can perform a driving control of the motor only when the estimated temperature is not larger than a predetermined value. A mode switching means switches the control unit and the estimated temperature calculating means between in a normal operation mode in which they can drive the motor and in a sleep mode in which electric power consumption thereof is smaller than in the normal operation mode in accordance with a predetermined condition while the motor is stationary. An activating means activates the estimated temperature calculating means in the sleep mode for a predetermined active time every time a predetermined sleep time is elapsed.