PURPOSE: To obtain an inexpensive manifold assembly which can withstand a high inner working pressure and can be fixed easily by providing an integral tank having a U-shaped cross section and a header plate of the same length as the tank.

CONSTITUTION: A manifold assembly 110 being used in an inner pressure heat exchanger having a plurality of parallel tubes is provided with an integral tank 120 having a U-shaped cross section, and an integral header plate 150 of the same length as the tank 120. The header plate 150 is inserted into the tank 120 on the inside of the fringe part 134 thereof. The flange 142 of the tank 120 is bent inward to engage with the header plate 150 along the entire length thereof. The header plate 150 and the tank 120 are formed of an aluminum material and an aluminum alloy material suitable for brazing to a furnace and at least one abutting face is formed of a low temperature crack brazing material.