A heat exchanger includes: a first flow passage for an engine coolant; a second flow passage for an engine oil; a third flow passage for a transmission oil; and plural plates that partition the first, the second and the third flow passage. The first flow passage is configured to allow the engine coolant to be heat-exchanged with both the engine oil and the transmission oil via the plates. The second flow passage is arranged in the same layer with the third flow passage. The first flow passage is arranged in a different layer from the layer of the second and the third flow passage. The third flow passage is disposed on an upstream side and second flow passage is disposed on a downstream side in a flow direction of the engine coolant in the first flow passage.