Accepting the merits of the plate-type heat exchanger and supplementing the demerits of the multi-pipe heat exchanger, the oblong plate & shell heat exchanger has the heat plates, which are wrinkled in the oblong shape. As its center part in shape of round is extended into the oblong plate shape, the increased heat transfer length and area revolutionarily enhance the heat transfer efficiency. It is a high-efficiency compact and fully-welded heat exchanger of the next generation, that can be used in high-temperature and high-pressure conditions, without a gasket. Characteristics The wrinkles of the heat transfer plates generate turbulent at a low Reynolds number, and the total heat transfer coefficient is 3000 kcal/m2h ~ 6000 kcal/m2h (4~5 times higher than that of the multi-pipe heat exchanger). The fully-welded structure of the heat transfer plates and the shell allows the maximum usable pressure up to 80 kg/cmG. As it is the fully-welded type not using a gasket, the available temperature is 600 (up to 900 in maximum). The price is lower than that of the multi-pipe heat exchanger. Its small size (1/4 of the multi-pipe heat exchanger) reduces the required space for installation and the weight, and the fully-welded type without requiring periodical replacement of a gasket minimizes the maintenance cost. Also, the small-sized condenser for a large-capacity vapor provides prominent effects.