A radiator includes a core unit, which includes a flow inlet which coolant enters, a flow outlet from which the coolant exits, a plurality of coolant pathways including at least an outer coolant pathway, an inner coolant pathway, a branching point, and a merging point, the outer coolant pathway being disposed to surround the inner coolant pathway, the coolant being divided at the branching point and merging at the merging point, and a connecting pathway to connect between the merging point of the outer coolant pathway and the branching point of the inner coolant pathway, wherein the flow inlet is in communication with a branching point of an outermost one of the plurality of coolant pathways, and the flow output is in communication with a merging point of an innermost one of the plurality of coolant pathways.