The invention concerns a rotary single-phase electromagnetic servo actuator consisting of a rotary actuator designed to move a mobile member along a limited travel, including a 2N pole stator structure, N being equal to 1 or 2, and at least one field coil, said stator structure being made of a material with high magnetic permeability, and a rotor having a ferromagnetic yoke and a thin magnetized portion consisting of 2N pairs of axially magnetized poles, in alternate directions and a rotor angular position sensor. The invention is characterized in that the position sensor has a magnetic field emitter integral with the yoke and a receiver for the magnetic field stationary relative to the stator structure.