Heat exchange element

A heat exchange element formed by stacking a plurality of heat transfer plates, wherein

• each of the heat transfer plates includes:
• a heat exchanger adapted to allow air passing through one side in a stacking direction of a plurality of the heat transfer plates and air passing through another side in the stacking direction to pass through in directions facing each other to cause heat exchange;
• a header provided on one side and another side with the heat exchanger interposed therebetween when viewed along the stacking direction;
• and
• a joining edge provided along a side of the heat exchanger that is not in contact with the header, wherein
• the joining edge of a plurality of the stacked heat transfer plates are in contact with each other and joined by ultrasonic welding, and
• the joining edge is formed with a first convex portion that protrudes along the stacking direction and a concave portion into which the first convex portion of an adjacent heat transfer plate among the heat transfer plates is fitted.