PURPOSE: To improve the responsiveness of the fed portion of pressure oil that operates according to operation force from the outside to a master cylinder and improve the longevity of the master cylinder and also facilitate the formation of the master cylinder.

CONSTITUTION: This master cylinder is equipped with a hydraulic cylinder 3; and a reserver 6 that can feed oil to a pressure chamber 4 in the hydraulic cylinder 3. A space surrounded with the cylinder tube 8 of the hydraulic cylinder 3 and a piston 10 is made to be the pressure chamber 4, and the piston 10 is made up of first and second cups 20, 21 that are positioned separately from each other axially. A relief port 41 to connect the reserver 6 inside and the pressure chamber 4 mutually is provided, and at the same time a supply port 43 to connect the reserver 6 inside and a supply chamber 42 between the first and second cups 20, 21 mutually is provided. A hydraulic filter 45 is provided so as to fill the relief port 41.