A downflow reboiler-condenser which can distribute and introduce an evaporating fluid (fluid to be evaporated) uniformly and securely into evaporation passages and which can also achieve simplification of its structure and reduction in the fabrication cost. This reboiler-condenser is provided with a reservoir 36 above a heat exchanger core 34 and with liquid distributors 37 located above evaporation passages 33 respectively. The liquid distributors 37 distribute the evaporating fluid collected in the reservoir 36 into the evaporation passages 33 uniformly.