A heat exchanger includes a plurality of flat tubes, a header collecting tube connected to the flat tubes, and fins joined to the flat tubes. The header collecting tube includes a first partition member partitioning an internal space into upper and lower internal spaces, a second partition member partitioning the upper internal space into first and second spaces, an inflow port formed at a bottom part of the first space, an upper communicating passage, a lower communicating passage. A third partition member partitions the lower internal space into an ascension space and an inflow space. A lower communicating port allows refrigerant to pass from the inflow space to the ascension space. The lower communicating port and the refrigerant passages of the flat tubes that are connected to the lower internal space are arranged so as not to overlap each other as viewed along the longitudinal direction of the flat tubes.