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.