A reserve tank has a container, an outlet component, and an inlet component. The outlet component and the inlet component are mounted on the container. The outlet component has an open end located at a center of the container. The inlet component has a branch portion mounted in the container and an inlet channel in the branch portion. Therefore, when the reserve tank is disposed obliquely, even though the reserve tank is not full of a working liquid and contains some gas, the gas can hardly flow into the open end of the outlet component. In addition, if some gas enters the container through the inlet channel and thus forms bubbles, the bubbles may move upward along part of the branch tunnels extending upward, so the entering bubbles are still far from the open end.