An electric power tool receives an input power from an electric power source and converts the input power to a driving power to drive an electric motor. The electric power tool further includes a manual control mechanism, a magnetic control element and a power modulation circuit. The manual control mechanism includes a trigger portion movable by depressing of a user and a magnetic element movable with the trigger portion. The magnetic control element outputs an output control signal in proportion to alterations of a magnetic field caused by movements of the magnetic element. The power modulation circuit gets the input power and modulates to the driving power controlled by the output control signal to drive the electric motor. Thus by depressing the trigger portion, output power of the electric motor can be controlled to provide precise control of rotational speed and torque alterations.