An actuating device is part of a bicycle hydraulic operating system that also includes an additional actuating device and a hydraulic operated device. The hydraulic operated device includes a slave cylinder fluidly connected to an additional master cylinder of the additional actuating device such that operation of an additional operating member of the additional actuating device moves the slave piston. The actuating device includes an operating member, a master cylinder, a master piston and a fluid port. The fluid port fluidly connects the master cylinder to the slave fluid port such that operation of the operating member moves the slave piston. The actuating device has no fluid reservoir. The master cylinder of the actuating device is fluidly connected to the additional master cylinder of the additional actuating device at a point upstream of the fluid port with respect to a flow of hydraulic fluid towards the hydraulic operated device.