A heat management system includes a reservoir tank which stores a coolant and can replenish, with the coolant, a coolant line connected to the reservoir tank; a flow path transition valve which is connected to the downstream side, according to the flow direction of the coolant, of the reservoir tank and can control the flow direction of the coolant; and a coolant circulation pump which is connected to the downstream side, according to the flow direction of the coolant, of the flow path transition valve and pumps the coolant along the coolant line, wherein, through the layout structure of the reservoir tank, flow path transition valve, and coolant circulation pump, the distance between parts constituting a coolant system of a vehicle is minimized, and the overall flow of the coolant is formed in the direction of gravity, and, thereby, a pressure drop of the coolant can be reduced.