Abstract: A reserve tank includes a gas-liquid separator, a flow inlet portion, a flow outlet portion, and a projection shaped in a tubular form. The gas-liquid separator is shaped in a bottomed tubular form and is centered on a predetermined axis. The flow inlet portion is configured to conduct coolant into an inside of the gas-liquid separator. The flow outlet portion is configured to discharge the coolant from the inside of the gas-liquid separator. The projection extends along the predetermined axis from a bottom wall at the inside of the gas-liquid separator. An inner space of the projection opens to an inner space of the gas-liquid separator at a distal end portion of the projection.