PURPOSE: To improve the efficiency of the evaporation effect of water by provid ing a unit condensing device which can cover part of a solar heat absorbing plate and constructing the titled device in such a manner that the solar heat absorbing plate and the unit condensing device can be relatively moved.

CONSTITUTION: The solar heat absorbing plate 1 disposed horizontally or inclinedly and at least one unit condensing device 2 which can cover part of the solar heat absorbing plate 1 are provided to the device. The device is so constructed that the solar heat absorbing plate 1 and the unit condensing device 2 can be relatively moved. The unit condensing device is positioned onto the solar heat absorbing plate of the part where the solar heat is absorbed in the above-mentioned constitution. The sea water is then run on the above-mentioned part and is condensed. The absorption of the solar heat begins again in the above-mentioned part if the device 2 is relatively moved from the above- mentioned part of the plate 1 cooled by such operation. The solar heat is thor oughly absorbed before the movement of the device 2 is the part to which said device moves. The condensation operation similar to the above-mentioned operation is thereupon executed again. The fresh water is continuously and effectively recovered by continuing such operation.