A hydraulic braking system includes: a cylinder device including a pressurizing piston, a rear chamber, and a front pressure chamber on opposite sides of the pressurizing piston; a brake cylinder coupled to the front pressure chamber; a regulator including a control piston, an input chamber provided at a rear of the control piston, and an output chamber coupled to the rear chamber in front of the control piston; and an input-hydraulic-pressure control device including a high-flow-rate supply unit configured, when an operation of the regulator is started, to supply the working fluid to the input chamber at a set flow rate; and a low-flow-rate supply unit configured, when the supply is finished, to supply the working fluid to the input chamber at a flow rate less than the set flow rate.