PURPOSE: To shield a buffer chamber from a brake pipe by a method wherein a throttle unit which provides a throttle position for a brake pipe or a brake pipe room is provided in a hollow hole.

CONSTITUTION: A throttle insertion unit 11 supported by a shoulder-type step part 10 through a circulating ring 12 is pushed into a hollow hole 9. The throttle insertion unit 11 restricts a free space 13 linked with a passage 14 in a buffer chamber 8. When antilock adjustment is practiced, a magnet valve 20 is switched to a cut-off position and brake liquid is discharged from a wheel brake cylinder 5 through a feedback pump or a feedback pipe 18. The feedback pump 15 conveys the brake liquid into the buffer chamber 8 or the free space 13 and the brake liquid is made to flow out of the chamber 18 or the space 13 again through a throttle position 25. With this constitution, vibration caused by liquid power fluctuation can be attenuated and noise can be suppressed.