Master cylinder

A master cylinder comprising:

• a stepped cylinder having a large diameter cylinder portion and a small diameter cylinder portion;
• a stepped piston having a large diameter piston portion slidably inserted into the large diameter cylinder portion of the stepped cylinder and a small diameter piston portion slidably inserted into the small diameter cylinder portion of the stepped cylinder;
• a reverse-flow-checking opening and closing portion for partitioning an inside of the stepped cylinder into a large diameter pressurizing chamber on a large diameter piston portion side and a small diameter hydraulic chamber on a small diameter piston portion side, and permitting a brake fluid to flow only from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side;
• a control valve device connecting with the large diameter pressurizing chamber, the small diameter hydraulic chamber and a reservoir, and releasing by a control valve body a hydraulic pressure in the large diameter pressurizing chamber to the reservoir side such that the hydraulic pressure in the large diameter pressurizing chamber is gradually reduced in accordance with a rise in a hydraulic pressure in the small diameter hydraulic chamber;
• and
• a check valve device having a check valve chamber for communicating with a relief passage to release a hydraulic pressure in the large diameter pressurizing chamber via the control valve device to the reservoir and with the small diameter hydraulic chamber, respectively, and a check valve body accommodated in the check valve chamber for permitting a brake fluid to flow from the relief passage to the small diameter hydraulic chamber and preventing flow of the brake fluid flow in the reverse direction.