A vehicle brake system comprising: an input device for detecting an amount of operation by an operator; and an electric brake actuator for generating a first brake hydraulic pressure at least on the basis of an electric signal according to the amount of operation, wherein the input device is integrally formed to include a master cylinder and a stroke simulator, the master cylinder generating a second brake hydraulic pressure in response to an input by a piston connected to a brake operation element, and the stroke simulator being integrally provided with the master cylinder as well as communicating with the master cylinder via a hydraulic communication path (58b, 58c), wherein the stroke simulator includes a simulator piston and a simulator accommodation chamber which accommodates the simulator piston therein, the simulator piston being movable against an urging force of an urging member (66a, 66b) by being driven by the second brake hydraulic pressure in the simulator accommodation chamber, and wherein each of a master cylinder accommodation chamber of the master cylinder and the simulator accommodation chamber is closed toward the opposite side of the brake operation element, characterized in that the simulator accommodation chamber includes an opening portion on the same side that the master cylinder accommodation chamber includes an opening portion for inserting pistons (40a, 40b) which allows the simulator piston to be inserted into the simulator accommodation chamber from the side on which the brake operation element is disposed, wherein a receiving member for receiving an input load to the simulator piston is disposed on the opening portion of the simulator accommodation chamber, and the receiving member is held in a simulator housing by a holding ring which is detachable with the simulator housing in a state that the urging member (66a, 66b) and the simulator piston are accommodated in the simulator accommodation chamber, wherein the input device is mounted on a dashboard which covers the opening portion in a mounted state of the input device, and the master cylinder and the stroke simulator are arranged side by side, wherein to the input device is attached a sensor valve unit located on the opposite side of the master cylinder accommodation chamber with respect to the simulator accommodation chamber, and wherein the sensor valve unit at least comprises first, second and third shutoff valves (60a, 60b, 62) and two pressure sensors (Pm, Pp) for detecting a hydraulic pressure on an upstream side of the first shutoff valve 60a and a hydraulic pressure on a downstream side of the second shutoff valve 60b. an input device for detecting an amount of operation by an operator; and an electric brake actuator for generating a first brake hydraulic pressure at least on the basis of an electric signal according to the amount of operation, wherein the input device is integrally formed to include a master cylinder and a stroke simulator, the master cylinder generating a second brake hydraulic pressure in response to an input by a piston connected to a brake operation element, and the stroke simulator being integrally provided with the master cylinder as well as communicating with the master cylinder via a hydraulic communication path (58b, 58c), wherein the stroke simulator includes a simulator piston and a simulator accommodation chamber which accommodates the simulator piston therein, the simulator piston being movable against an urging force of an urging member (66a, 66b) by being driven by the second brake hydraulic pressure in the simulator accommodation chamber, and wherein each of a master cylinder accommodation chamber of the master cylinder and the simulator accommodation chamber is closed toward the opposite side of the brake operation element, characterized in that the simulator accommodation chamber includes an opening portion on the same side that the master cylinder accommodation chamber includes an opening portion for inserting pistons (40a, 40b) which allows the simulator piston to be inserted into the simulator accommodation chamber from the side on which the brake operation element is disposed, wherein a receiving member for receiving an input load to the simulator piston is disposed on the opening portion of the simulator accommodation chamber, and the receiving member is held in a simulator housing by a holding ring which is detachable with the simulator housing in a state that the urging member (66a, 66b) and the simulator piston are accommodated in the simulator accommodation chamber, wherein the input device is mounted on a dashboard which covers the opening portion in a mounted state of the input device, and the master cylinder and the stroke simulator are arranged side by side, wherein to the input device is attached a sensor valve unit located on the opposite side of the master cylinder accommodation chamber with respect to the simulator accommodation chamber, and wherein the sensor valve unit at least comprises first, second and third shutoff valves (60a, 60b, 62) and two pressure sensors (Pm, Pp) for detecting a hydraulic pressure on an upstream side of the first shutoff valve 60a and a hydraulic pressure on a downstream side of the second shutoff valve 60b.