PURPOSE: To dispense with or miniaturize a heat exchanger which is separately provided to heat a raw liq., to reduce the setting space and to improve the heat efficiency by furnishing a heat source fluid passage partitioned by a heating heat-transfer plate in a raw liq. passage or in the vicinity of the passage.

CONSTITUTION: Two nonpermeable condensing heat-transfer plates 8 are respectively provided on the outside of two permeable membranes 7, a liq. condensate passage 9 is formed in between, two nonpermeable heating heat-transfer plates 13 are inserted between both permeable membranes 7 to form a heat source fluid passage 12, a raw liq. passage 14 is formed between the heating heat- transfer plate 13 and the permeable membrane 7 and a laminated unit 6 is formed. Plural units are laminated. A high-temp. cooling fluid from a diesel engine is passed through the heat source fluid passage 12 as the heat source fluid. Meanwhile, seawater is supplied into a cooling liq. passage 16 from a supply hole 18 to cool the heat-transfer plate 8 and the heated seawater is sent into the raw liq. passage 14 from the outlet hole 22 through a pipeline 28 and a supply hole 19. The heat is exchanged with the heat source fluid through the heat-transfer plate 13 and the vapor of the heated seawater is permeated through the permeable membrane 7.