a hydraulic block provided with a main bore formed therein in an axial direction;

a first piston having one side inserted into the main bore to be displaceable and the other side exposed to an outside of the hydraulic block and connected to a brake pedal;

a mounting block provided with a sub bore formed therein in the axial direction and the sub bore where the first piston is inserted thereinto and passes therethrough to be displaceable and a connection port connecting the sub bore and a reservoir;

a cap provided on one side of the first piston; and

a gap flow path formed by a gap between the first piston and the cap so that a first liquid pressure chamber partitioned by the first piston communicates with the connection port on the main bore,

wherein the first piston includes a mounting portion recessed in one side thereof in an axial direction,

wherein the cap includes:

a main body inserted into the mounting portion; and

a flange portion extending in a radial direction from one end of the main body, and

wherein the gap flow path includes:

a first slit recessed in an outer circumferential surface of the main body in the axial direction; and

a second slit recessed in the radial direction in the other side facing one end of the first piston on the flange portion and connected to the first slit.