Abstract: In a header plate structure of heat exchangers having a core divided in plurality, a flat tube is inserted into each of the tube insertion holes having a burring, which is formed in a header plate; the flat tube is joined at an inner surface in the vicinity of a top portion of the burring; a burring with height H1 is formed to a long side portion of a dummy tube insertion hole; and a burring with height H2 is formed to a long side portion of an end portion tube insertion hole adjacent to the dummy tube insertion hole, in which height H2 of the burring of the end portion tube insertion hole has been formed higher than the height H1 of the burring of the dummy tube insertion hole.