A heat exchanger provided with a plurality of plate-like fins 2 arranged in parallel with a predetermined interval and a plurality of flat-shaped heat transfer pipes 3 inserted in a direction orthogonal to said plate-like fins 2 and through which a refrigerant flows, in which said heat transfer pipe 3 has an outside shape with a flat outer face arranged along an air flow direction and a section substantially in an oval shape and first and second refrigerant flow passages 31a, 31b made of two symmetric and substantially D-shaped through holes having a bulkhead 32 between the two passages inside, which is bonded to said plate-like fin 2 by expanding diameters of said first and second refrigerant flow passages 31a, 31b by a pipe-expanding burette ball.