PURPOSE: To eliminate separation of wick and generation of scale and to improve thermal diffusion efficiency of a thermal diffusion type multiple effect distillation apparatus by installing partition walls and porous liquid impermeable membranes parallelly and alternately with appropriate distance therebetween.

CONSTITUTION: Partition walls 1 and porous liquid impermeable membranes 2 made of polytetrafluoroethylene are installed parallelly with a small distance alternately to construct a multilayered body having plural numbers of closed spaces and the surroundings are enclosed with a heat insulating material Feed liquid in a feed liquid feeding space 6 in the outermost layer is evaporated by heating with solar rays absorbed selectively by the selective absorption membrane 3 provided to the partition wall 1 at the outermost layer. Evaporated vapor permeates a porous membrane 2 at the rear side, enters a distilled vapor collecting space 10 at the outermost layer, and condenses by contacting with the partition wall 1 at the next layer to form distilled liquid. Feed liquid in the feed liquid feeding space 6 in the next layer is heated by the latent heat of condensation generated in this stage. The procedure is repeated in the succeeding layers, and concentrated liquid and distilled liquid are obtd. from an outlet 9 of the concentrated liquid and an outlet 11 of distilled liquid.