A plate type heat exchanger employing flat tubes, which can be manufactured easily and which have a high heat exchange performance includes a thin strip-shaped metal plate cut in the width direction and having remaining small connected portions and many cut portions disposed at fixed intervals in the longitudinal direction slits are formed in both sides of the cut potions having the same center. The strip-shaped metal plate is bent at the connected portions in a zigzag manner to form an aggregation of fin elements, and the flat tubes are engaged with the front and rear sides of the aggregation of the fin elements.