PURPOSE: To secure brake fluid pressure reducing function at the time of anti- lock control without strictly limiting the quantity of a brake fluid leaking to a low pressure reservoir at the normal braking time.

CONSTITUTION: The valve opening pressure of the intake valve and delivery valve of plunger type pumps 28, 38 is set lower than the lowest fluid pressure of the brake fluid chambers of low pressure reservoirs 23, 33, and at the time of releasing brake operation, the brake fluid in the low pressure reservoirs 23, 33 is returned to a master cylinder 12 through the inside of the plunger type pumps 28, 38.