A heat exchanger includes: flat pipes disposed in multiple stages in a stage direction corresponding to an up-down direction; and fins that partition a space between adjacent two of the flat pipes into air flow passages through which air flows. Each of the flat pipes includes a passage for a refrigerant inside thereof. The flat pipes are divided into heat exchange paths arrayed in multiple stages in the stage direction. One of the heat exchange paths that includes a lowermost one of the flat pipes is defined as a first heat exchange path. A length of the passage from a first end to a second end of a flow of the refrigerant in each of the heat exchange paths is defined as a path effective length.