A heat exchanger apparatus for a vehicle includes a heat exchanging unit including one or more plate units in which two or more plates are stacked to form different connection channels and exchanging heat with each other while different operating fluids pass through the respective connection channels in the heat exchanging unit, an upper cover mounted on one side of the heat exchanging unit, and including a plurality of inlets that introduce each operating fluid into the heat exchanging unit and are interconnected with the respective connection channels, and a lower cover mounted on the other side of the heat exchanging unit, and including a plurality of outlets that are interconnected with the respective connection channels so as to discharge the each operating fluid passing through the heat exchanging unit.