A power door opening and closing device comprising: an actuator that assists an operating force to open and close a door supported to a vehicle body, wherein the actuator has a casing within which a motor, a first planetary gear mechanism, a second planetary gear mechanism, a third planetary gear mechanism, an intermediate shaft and an output shaft are disposed, wherein a rotating force of a rotary shaft of the motor is transmitted to the intermediate shaft and the output shaft on the same axis while slowing down, and wherein the door is opened or closed by rotating the rotary shaft of the motor in a predetermined direction via an arm fixed to an end of the output shaft, the arm being coupled to a door hinge via a link; and characterized in that the device comprises: a unit-in sensor disposed in the casing of the actuator for generating a pulse with opening and closing motion of the door wherein the unit-in sensor is constituted by a magnetic ring rotating together with the intermediate shaft and a sensor base plate having a sensor facing the magnetic ring; an angular velocity sensor disposed at an end of the door to detect opening and closing motion of the door; and a control that carries out opening and closing control of the actuator when the control determines the door is manually operated, wherein the control comprises a main control portion that is a microprocessor that performs a set of control treatment according to instructions of control program stored in an internal memory, wherein the control has input ports into which a signal is supplied from the unit-in sensor and the angular velocity sensor, and wherein the main control portion comprises a determining portion for determining whether the door is operated manually based on a detecting signal from the unit-in sensor and the angular velocity sensor; wherein, when the motor is at rest, the determining portion of the control determines that the door is manually operated when the unit-in sensor generates a pulse signal of more than a predetermined number or when the angular velocity sensor generates an angular variable signal to detect that the end of the door moves in an opening or closing direction. a unit-in sensor disposed in the casing of the actuator for generating a pulse with opening and closing motion of the door wherein the unit-in sensor is constituted by a magnetic ring rotating together with the intermediate shaft and a sensor base plate having a sensor facing the magnetic ring; an angular velocity sensor disposed at an end of the door to detect opening and closing motion of the door; and a control that carries out opening and closing control of the actuator when the control determines the door is manually operated, wherein the control comprises a main control portion that is a microprocessor that performs a set of control treatment according to instructions of control program stored in an internal memory, wherein the control has input ports into which a signal is supplied from the unit-in sensor and the angular velocity sensor, and wherein the main control portion comprises a determining portion for determining whether the door is operated manually based on a detecting signal from the unit-in sensor and the angular velocity sensor; wherein, when the motor is at rest, the determining portion of the control determines that the door is manually operated when the unit-in sensor generates a pulse signal of more than a predetermined number or when the angular velocity sensor generates an angular variable signal to detect that the end of the door moves in an opening or closing direction.