A heat exchanger, in particular a supercharging air cooler for a motor vehicle engine, comprises a housing (11) provided with a heat exchange bundle (3), a collector (13) of a cooling liquid circulating in the heat exchange bundle (3), and a collector plate (15) forming a side wall of the heat exchanger housing (11) and of the cooling liquid collector (13). The collector plate (15) is provided with orifices (27) communicating with the cooling liquid circulation pipes of the bundle (3). The collector plate (15) comprises a flat connecting part (33a, 35a) fixed to the cooling liquid collector (13) opposite edges of the orifices (27). The flat connecting part (33a, 35a) is contiguous to at least one of the edges.