A hydraulic operating device for a small vehicle including a bicycle is basically provided with a base member, an operating member, a piston, a handlebar fixing structure and a hydraulic reservoir tank. The base member includes a cylinder having a cylinder bore. The operating member is pivots about a pivot axis to move the piston within the cylinder bore. The handlebar fixing structure defines a handlebar arrangement area. The hydraulic reservoir tank has a hydraulic fluid chamber fluidly connected to the cylinder bore. The cylinder defines a hydraulic pressure chamber with a space between the piston and a fluid outlet port of the cylinder. The hydraulic reservoir tank is partially disposed on a first side of the handlebar fixing structure while the hydraulic pressure chamber is disposed on a second side of the handlebar fixing structure as view in the pivot axis direction.