A motor actuator for actuating a driven member includes a control unit and a brushless motor, which includes a coil, a magnet and a hall element. The coil generates a magnetic field when being energized. The magnet rotor is rotatable in the magnetic field generated by the coil. The hall element detects a variation in the magnetic field due to rotation of the magnet rotor. Then, the hall element outputs an output signal according to the variation in the magnetic field. The control unit detects a relative position between the magnet rotor and the coil based on the output signal outputted from the hall element, and controls energization of the coil based on the relative position. Furthermore, the control unit detects a location of the driven member, and controls the brushless motor to drive the driven member based on a rotation amount of the magnet rotor.