To provide a position detecting apparatus and a valve driving apparatus of a rotary solenoid capable of more accurately detecting the position of a rotating shaft.

A valve actuator 40 is provided with a rotor 42 arranged with permanent magnets 42b, 42c of N pole and S pole as well as a rotary shaft 41 which rotates integrally with it, and a first coil 47 and a second coil 48 generating magnetic field in a first direction and a second direction to yokes 43-45. A position detecting apparatus detects the position of the rotor 42, by integrating induced voltage generated in the second coil 48 with an integrating circuit 64b, as well as rotates the rotor 42 toward the first position by generating magnetic field in the first direction in the yokes 43-45 by energizing the first coil 47. Integration of the induced voltage by the integrating circuit 64b is made effective by a relay 65b only when the first coil 47 is energized.