A hydraulic operating apparatus for a small vehicle, including a bicycle, comprises a housing, a piston, a mounting assembly, a lever, and a fluid reservoir tank. The housing includes a cylinder bore extending along a cylinder axis. The piston is movably disposed within the cylinder bore. The mounting assembly is configured to mount the housing to a handlebar of the small vehicle. The mounting assembly defines a handlebar mounting axis that is not perpendicular to the cylinder axis in a mounted state where the housing is mounted to the handlebar. The lever is pivotally mounted to the housing and configured to move the piston within the cylinder bore in response to a movement of the lever. The fluid reservoir tank has a lid opening. The lid opening is configured to face a center plane that passes through a geometric center of the handlebar and that is perpendicular to the handlebar mounting axis, in the mounted state.