A heat exchanger adopts a four-pass structure, including two rows of tubes, a first upper tank portion communicating with the upper end of one of the tube rows, a second upper tank portion communicating with the upper end of the other tube row, a first lower tank portion communicating with the lower end of the one tube row, a second lower tank portion communicating with the lower end of the other tube row, a communicating passage that communicates between first ends of the first and second upper tank portions a partition partitioning each of the first and second upper tank portions, inflow and outflow ports communicating with the other ends of the first and second upper tank portions. The inflow port opening is smaller and has a higher center than the outflow port opening.