A heat exchanger includes a plurality of plates that is stacked together to constitute first flow passages, second flow passage, third flow passage, fourth flow passage and fifth flow passage. An engine coolant flows through the first flow passages. An engine oil flows through the second flow passages and fourth flow passages. A transmission oil flows through the third flow passages and fifth flow passages. Triple-flow-passage arrangement layers in each of which each first, second, and third flow passages are disposed, and dual-flow-passage arrangement layers in each of which each fourth and fifth flow passages are disposed are alternately arranged such that flow passages of each same type are not overlaid with one another in a stacking direction of the plates.