The heat exchanger (1) comprises: two header pipes (2),(3) arranged in parallel with an interval therebetween; a plurality of flat tubes (4) which are arranged between the header pipes and which place coolant paths (5) provided therein in communication with the interior of the header pipes; a plurality of fins (6) attached to the flat surface of each flat tube; and side sheets (10U), (10D) attached to an outside of the fins (6aU), (6aD), which are positioned farthest outward among the plurality of fins. The side sheet (10D) positioned in the bottom part of the heat exchanger (1) has a plurality of notches (11) formed at intervals from each other on the edge of the side where condensed water collects in the heat exchanger (1). The notches are each provided with a width sufficient for covering the interval pitch (P) of the fin by several pitch lengths.