WORKING FLUID FLOW CONTROL VALVE FOR MASTER CYLINDER, MASTER CYLINDER COMPRISING SAME, AND BRAKE DEVICE EMPLOYING MASTER CYLINDER

[Problem] Provided is a master cylinder hydraulic fluid flow control valve which can effectively decrease a pressure receiving area of a floating valve element when the floating valve element is seated on a valve seat, can favorably maintain a sealing function of a sealing member, and can suppress the increase of the number of assembling operation man-hours. [Means for Resolution] A floating valve element 26a is vertically movably accommodated in a master cylinder connecting nipple portion 6b 2 , 6c 2 which is hermetically mounted on a tandem master cylinder 4 by sealing members 23, 24 and forms a fluid passage between a reservoir tank and a tandem master cylinder 4 therein, and a valve seat 26b on which the floating valve element 26a is seatable is arranged in the master cylinder connecting nipple portion 6b 2 , 6c 2 .