PURPOSE: To make necessary braking pressure demonstrable irrespective of operation of a braking hydraulic pressure generating means by connecting a hydraulic pressure supply source to a control room being partitioned off by a spool valve body of a traction control means at time of traction controlling, and moving the spool valve body to the side of an output chamber.

CONSTITUTION: In a traction control means 1 being interposed between a master cylinder M and a braking device B, a spool valve body 8 is fitted in a housing 7 with an input port 6 leading to an output port 2 of the master cylinder M. An output chamber 9 leading to a braking hydraulic chamber 5 of the braking device B and a control room 10 being partitioned to the opposite side both are formed in the housing 7 by the spool valve body 8, and this control room 10 is made connectible to a hydraulic supply source 14 and a reservoir R via a selector valve means V. In addition, a ring groove 12 to be interconnected to the input port 6 is formed in the spool valve body 8 in the state that this spool valve body shifts to the side of the control room 10 at its maximum, while there are provided with interconnecting holes 13 which interconnect this ring groove 12 to the output chamber 9.