Provided is a stroke simulator capable of suppressing occurrence of inclination of a piston with respect to a sliding surface formed in a cylinder. The stroke simulator includes a simulator piston which is displaced by sliding on a sliding surface formed in a first cylinder, and a first return spring which is housed in the first cylinder and applies, to the simulator piston, a reaction force which is generated by an elastic deformation of the spring under a pressing force due to a displacement of the simulator piston, and generates the reaction force which is applied to the simulator piston as a brake reaction force for a brake operating element. The stroke simulator is characterized in that a cup seal for sealing a gap formed between the sliding surface and the simulator piston is mounted in the middle in the axial direction of the sliding surface.

An object of the present invention is to provide a brake apparatus that can achieve a characteristic capable of increasing a pressure with high responsiveness without relying on a discharge capability of a pump. According to an aspect of the present invention, a brake apparatus includes an operation rod configured to be activated according to an operation of a brake operation member and having a first diameter, a stepped piston including an intermediate-diameter portion having a larger diameter than the first diameter on one side, a large-diameter portion having a larger diameter than the diameter of the intermediate-diameter portion, and an insertion hole in which the operation rod is relatively displaceably inserted from an axial direction, a first pressure chamber formed between the first diameter and the intermediate-diameter portion, and a second pressure chamber formed between the intermediate-diameter portion and the large-diameter portion. The brake apparatus controls an amount of the brake fluid to be supplied to the first pressure chamber and the second pressure chamber, and increases the amount of the brake fluid to be supplied to the second pressure chamber when a detected state is a pressure increase request requiring high responsiveness.

An actuating unit for a brake system, comprises a pedal connection element that charges a booster piston with an actuating force. An elastically deformable reaction disk, absorbs the actuating and boosting forces of the booster and releases the sum of said forces to a working piston. An electrically controllable pressure supply device outputs pressure which acts upon the booster piston. The actuating unit further comprises an extension arm for detecting the differential path between the pedal connection element and the booster piston and a sensor device that detects the differential path. An electronic control unit receives the signals from the sensor device and uses said signals for controlling the pressure supply device. Differential path information is transported by the extension arm to a location near the sensor device that is radially and axially offset by the reaction disk.