A heat-exchanging plate member has a pair of heat-exchanging plates, each of which has projection ribs and fluid passage forming portions arranged alternately. The pair of plates are connected to each other in a manner that the projection ribs formed in the plates, respectively, face outwardly with each other, and the projection ribs formed in one of the plates are connected to the fluid passage forming portions formed in the other of the plates, respectively, at a temperature where the strength of material is not lowered in a connecting process.