PURPOSE: To simplify construction of a device for treating waste liquid of photographic processing by providing a closed space formed from moisture permeable waterproof film in waste liquid and a cooling means for condensing water vapor in the closed space which has passed through said film.

CONSTITUTION: A heat exchange means 13 is provided in a space 12, whereby moisture contained in the air in the space 12 is cooled and condensed. In the means 15, a Peltier element 15 is provided in a frame 14 and air is blown to one side of the element 15 by means of a fan 16 and the heated air near the other side of the element 15 is exhausted to the outside of the means 13. The bottom plate 1a of a separation tank 1 is inclined, a cock 4 being provided at its lower end for discharging concentrated waste liquid 3 remaining in the tank 1. That is, since moisture is removed from the liquid 3, it is concentrated, but it is not solidified. The liquid 5 from which moisture has been removed is then drawn from the cock 4 to abandon it. Since the volume of the liquid 5 decreases as the moisture is removed, the amount of the liquid 5 to be disposed becomes smaller and hence it can be easily disposed.