In a radiator (5) in that core units (31 to 33) are arranged in parallel to each other on a lower main tank (16), and an upper main tank (15) is arranged at an offset position relative to the lower main tank (16) in the plan view, the upper main tank (15) is arranged at the substantially same height as upper auxiliary tanks (35) in the core units (31 to 33), and the side surface of each upper auxiliary tank (35) and the side surface of the upper main tank (15) are connected to each other by a coolant water conduit pipe (60). A coolant water inlet is arranged on the lower surface side of the upper main tank (15).