The invention relates to a hydraulic brake system which includes: a master cylinder including a pressurizing piston; a brake cylinder for a hydraulic brake operable by a hydraulic pressure in a front pressure chamber defined in front of the pressurizing piston; and a rear-hydraulic pressure controller connected to a rear chamber defined at a rear of the pressurizing piston. The rear-hydraulic pressure controller controls a hydraulic pressure in the rear chamber and includes: a regulator, operable by at least one of the hydraulic pressure in the front pressure chamber and a control pressure controlled electrically, for supplying an output hydraulic pressure to the rear chamber; and a master-pressure-operating-state detector configured to, when the output hydraulic pressure is greater than a threshold value, detect that the regulator is in a master-pressure operating state in which the regulator is operated by at least the hydraulic pressure in the front pressure chamber.