To prevent the generation of noises and a drop in heat exchange performance, by reducing a path resistance of a fluid flowing through tanks.

Connection holes 15a provided in the top surfaces of tanks 6c are made as outward burring holes having bent-up parts 21 on the external side of the tanks 6c. In a state where connection parts 12c and 12d are inserted into the connection holes 15a, the tip rims of the connection parts 12c and 12d will not protrude inward from the internal surfaces of the tanks 6c. This can lower a resistance to a fluid flowing into the tanks 6c.