PURPOSE: To easily make it possible to select a case, in which humidity exchange is done, or a case, in which no humidity exchange is done, by a method wherein the positions of first wallboards and second wallboards are shifted so as to respectively separate suction air passages and exhaust air passages from each other through humidity exchange elements when humidity exchange is done, while the positions of the first wallboards and of the second wallboards are set so as to respectively separate the suction air passages and the exhaust air passages from each other through humidity nonexchange elements when no humidity exchange is done.

CONSTITUTION: First wallboards 3a and second wallboards 4a are bridgedly fixed in horizontal postures to a first frame body 8 and to a second frame body 9. The interval 15 between the wallboards 3a and the interval 16 between the wallboards 4a are set to be equal to the interval between humidity exchange elements 1 and 1 and to the interval between humidity nonexchange elements 2 and 2. In addition, on the respective exhaust sides of indoor air and of outdoor air, wallboards 3b and 4b are fixed respectively to frame bodies 10 and 11 at the mounting positions, which are respectively and correspondingly same as those of the wallboards 3a and 4a on the suction sides. The respective frame bodies 8, 9, 10 and 11, which are arranged on four peripheral planes, are connected integrally with one another and constituted so as to be freely and vertically slidable by means of a shifting means, such as proper lifting device or the like.