A radiator includes a heat exchanger, an upper auxiliary tank, a lower auxiliary tank, an upper main tank and a lower main tank. The upper auxiliary tank is mounted on an upper surface of the heat exchanger. The lower auxiliary tank is mounted on a lower surface of the heat exchanger. The upper main tank is arranged at the substantially same height as the upper auxiliary tank and at an offset position relative to the upper auxiliary tank in the plan view. The upper main tank is connected to the upper auxiliary tank via a coolant water conduit pipe, and has a coolant water inlet on a lower surface thereof. The lower main tank is arranged under the upper main tank at an offset position relative to the upper main tank in the plan view, and is connected to the lower auxiliary tank.