Abstract: A plate type heat exchanger has a plurality of tube units and a plurality of corrugated fins. Each of the tube units is formed by a pair of plates, namely a pair of plates are connected to each other by a brazing material at a connecting portion at an outer periphery of the plate and a center rib at a center axis of the plate. The center rib has an enlarged portion at the top end thereof in order to gather the molten brazing material toward the enlarged portion. The brazing at the center rib is started from the enlarged portion. Therefore a brazing defect is prevented from occurring at the top end of the center rib. Since the tube unit is effectively connected by brazing, the tube unit of the present invention has enough anti-pressure strength.