PURPOSE: To uniformly distribute the refrigerant to respective refrigerant passage openings so as to improve the heat exchanging capacity and efficiency by making the width of the primary and secondary refrigerant inlets and outlets narrower on both sides than in the center, and making the length of the respective refrigerant passage openings shorter on both sides than in the center.

CONSTITUTION: The width of the primary and secondary refrigerant inlets and outlets of the respective plates is made smaller on both sides than in the center. The width of the primary side refrigerant inlet 13 of the seal plate 11 is smaller on both sides 13b than in the center 13a. Further, the end of the primary side refrigerant opening 17 and the secondary side refrigerant opening 19 is made shorter on both sides than in the center so as to match the primary side and secondary side refrigerant passage openings of the respective refrigerant inlets and outlets of the seal plate 11. Therefore, the primary and secondary refrigerants flowing from the primary side and secondary side inlet pipes enter the primary and secondary inlets to be uniformly distributed to the respective primary and secondary refrigerant passage openings, and then from the respective refrigerant outlets to the respective refrigerant outlet pipes, and so, the heat exchanging capacity and efficiency can be improved.