Hydraulic bicycle actuating device

A bicycle hydraulic actuator 12 is basically provided with a base member 20, a piston 22, an operating member 24, a hydraulic reservoir tank 26 and an intermediate wall 28th The base member 20 has a cylinder bore 44th The piston 22 is movably disposed in the cylinder bore 44th The operating member 24 is coupled to the piston 22 to move in the cylinder bore 44 the piston 22nd The hydraulic reservoir tank 26 is in fluid communication with the cylinder bore 44. The intermediate wall 28 is disposed in the hydraulic reservoir tank 26 and divides the hydraulic reservoir tank 26 in a hydraulic fluid chamber C1 and an air chamber C2. The air chamber C2 is located between the cylinder bore 44 and the hydraulic fluid chamber C1.