A fill-up device of a master cylinder is included in a hydraulic brake system for an automotive vehicle and generates a hydraulic pressure corresponding to an operation of a brake operating member. A coupled switching valve is switched by being mechanically coupled with movement of a piston relative to a housing. The coupled switching valve is in a first state where a fill-up chamber is in communication with a reservoir via a relief valve until the piston is advanced by a predetermined distance from a rearmost position, and switched to a second state where the fill-up chamber is in direct communication with the reservoir via the communication passage without the relief valve disposed therebetween when the piston is advanced by a distance larger than the predetermined distance. Thus, the hydraulic pressure in the fill-up chamber rapidly decreases, and the hydraulic pressure in pressure chambers rapidly increase.