Abstract: An actuator, a vehicle mounted radar device, and an automobile drive control system that employ a non-contact type potentiometer to detect a rotation angle of a rotary shaft. The non-contact type potentiometer includes a pair of planar magnets disposed opposite and parallel with respect to each other on a U-shaped magnetic yoke, the polarities of the magnets being arranged such that approximately parallel magnetic fields are formed around a magnetic detection element that is retained on a support shaft connected to a rotary shaft on an actuator, and can freely rotate relative to the stationary member. By rotating the rotary shaft on the actuator, a change in the output from the magnetic detection element occurs, thus allowing a rotation angle of the rotary shaft to be detected.