PURPOSE: To reduce the size of a device, by a method wherein, in an antilock control system having a proportioning valve, the proportioning valve and a valve mechanism, which performs antilock control, are contained in a single body.

CONSTITUTION: A device has a valve body 4 which is provided at both sides with cylinders 6 and 7 with a partition 5 nipped between the cylinders, and contains respectively within the cylinders 6 and 7 a valve piston part 10 and a control piston part 11 of a piston 9 having a through-part which extends through the partition 5. The valve piston part 10, functioning as a proportioning valve 12, and in a position, where the one-way valve 12 is deviated to the output liquid chamber (b) side, a ball valve 13 is separated from a valve seat 15 to open a communicating flow passage 17. The control piston part 11 is slid by means of a control oil pressure which is transmitted to a control oil pressure (c) through a pair of electromagnetic valves 20 and 21.