An electric power steering device according to the embodiment disclosed herein employs, in addition to a motor resolver of an electric motor for assisting the rotational manipulation of a steering shaft, first and second resolvers which are made different in the number of N-S pole pairs from each other each for detecting the rotational position of the steering shaft. The reduction gear ratio of a reduction gear mechanism of a ball screw mechanism driven by the electric motor is set so that a calculated value which is obtained by multiplying the reduction gear ratio with the number of pole pairs of a motor resolver represents a non-integer having a numerical value of the decimal place. Thus, it does not occur that calculated value becomes an integer which does not have any numerical value of the decimal place. As a result, it can be realized that the mechanical angle of the steering wheel which is calculated based on electrical angles of the first and second resolvers can be made not take the same value within any one-rotational range unit as that within another one-rotational range unit of four rotations in total of the steering wheel including two left rotations and two right rotations. Consequently, it becomes possible to detect the absolute rotational position of the steering wheel precisely, so that the motor for assisting the steering manipulation can reliably be controlled in dependence on the absolute rotational position of the steering wheel so precisely detected.