A heat exchanger includes left and right header tanks disposed in parallel; top and bottom side plates that couple respectively both ends of the pair of the header tanks; a first plurality of tubes connected between the pair of the header tanks at both ends that are disposed in a region nearer the bottom side plate as a condenser; and a second plurality of tubes that are disposed in a region nearer the top side plate as an oil cooler. Each tube in the second tubes has a cross-sectional shape identical to that of each tube in the first tubes and the top side plate is formed to have a squared U-shaped cross section so that a return pipe communicating with the second tubes can be disposed along a groove having the squared U-shaped cross section of the top side plate.