PURPOSE: To stably fill and retain a hydraulic liquid by improving the configuration of a compression spring in an accumulator and switching device for it in which a piston is displaced in sliding against the force of the compression spring to ensure the filling and retention of the hydraulic liquid.

CONSTITUTION: A pressure accumulating system to be connected with a branch pipe of a main hydraulic line leading from a pump to a brake for vehicle is filled with hydraulic liquid from a pump via a filling valve 8 and has an accumulator to stop the filling through closing of the valve 8 by the actuation of a control switch 7 to sense the filling condition. This accumulator has a housing 4 integrally provided with the switch 7 and valve 8, the housing 4 being fitted with a piston 2 in the extension part 12 thereof. A first molded member 3 is externally fitted on the piston 2 so as to surround it, with a compression spring 1 interposed between the first molded member 3 and a second molded member 5 straddling the member 3.