To provide an electrically powered brake system capable of performing a control of the braking force appropriate to a particular wheel rotational speed with high response and capable of being simplified in structure with no need to employ any hydraulic equipment and the related pipe lines, the electrically powered brake system includes an actuating unit 18 including a brake wheel 16 mounted on a vehicle wheel 1 and brake pieces 17 frictionally engageable with the brake wheel 16. A drive unit 19 is operable to translate a rotary output of an electric drive motor 20 into a rectilinear reciprocating motion by means of a ball screw mechanism 23, which rectilinear reciprocating motion is transmitted to the brake pieces 17 as a braking force. An operating unit 32 is operable to control the electric drive motor 20 according to manipulation of an operating member 31 such as, for example, a brake pedal. An anti-skid control device 35 is provided for regulating the braking force, exerted by the electric drive motor 20, in dependence on the number of revolutions of the vehicle wheel 1 during a braking effected by manipulation of the operating member 31. For a rotation detector 1 for detecting the number of revolutions of the vehicle wheel 1, the rotation detector 1 including a magnetic encoder 37 is employed.