A cylinder device for generating a hydraulic brake pressure according to an amount of manipulation of a brake manipulator, comprising: a base body in which a cylinder bore (11 a) and a reservoir union port are formed, where the cylinder bore has a bottom, the reservoir union port communicates with the cylinder bore, and a reservoir reserving brake fluid is connected to the reservoir union port; a piston inserted in the cylinder bore; an elastic member arranged between a bottom surface of the cylinder bore and the piston; a limiting member which projects into the cylinder bore and limits backward motion of the piston; the reservoir which has a fluid feeding portion having a tubular shape and being inserted in the reservoir union port; and a reservoir sealing member which has an annular shape and is externally fitted on the fluid feeding portion; wherein a communication bore and an installation bore each of which has an end opened in the bottom surface of the reservoir union port and another end opened in an inner circumferential surface of the cylinder bore are formed in the base body, and the limiting member is inserted in the installation bore (11 b); and the fluid feeding portion includes, a tip portion (41 b) arranged opposed to the limiting member, and a cutout portion (41 d) extended in an axial direction to a tip side of the fluid feeding portion, characterized in that the cutout portion is formed in the fluid feed portion to extend to the vicinity of the reservoir sealing member so as to exhaust air through a gap between the inner circumferential surface of the reservoir union port and the outer circumferential surface of the fluid feed portion into the reservoir. a base body in which a cylinder bore (11 a) and a reservoir union port are formed, where the cylinder bore has a bottom, the reservoir union port communicates with the cylinder bore, and a reservoir reserving brake fluid is connected to the reservoir union port; a piston inserted in the cylinder bore; an elastic member arranged between a bottom surface of the cylinder bore and the piston; a limiting member which projects into the cylinder bore and limits backward motion of the piston; the reservoir which has a fluid feeding portion having a tubular shape and being inserted in the reservoir union port; and a reservoir sealing member which has an annular shape and is externally fitted on the fluid feeding portion; wherein a communication bore and an installation bore each of which has an end opened in the bottom surface of the reservoir union port and another end opened in an inner circumferential surface of the cylinder bore are formed in the base body, and the limiting member is inserted in the installation bore (11 b); and the fluid feeding portion includes, a tip portion (41 b) arranged opposed to the limiting member, and a cutout portion (41 d) extended in an axial direction to a tip side of the fluid feeding portion, a tip portion (41 b) arranged opposed to the limiting member, and a cutout portion (41 d) extended in an axial direction to a tip side of the fluid feeding portion, characterized in that the cutout portion is formed in the fluid feed portion to extend to the vicinity of the reservoir sealing member so as to exhaust air through a gap between the inner circumferential surface of the reservoir union port and the outer circumferential surface of the fluid feed portion into the reservoir.