PURPOSE: To obtain a ventilating device favorable on the ventilation of a building for the building by smoothly conducting ventilation between each mutual permeable layer on the insides of an external facing material in an upper story and an external facing material in a lower story without interrupting each mutual permeable layer.

CONSTITUTION: In a boundary section between the upper story and lower story of a building, a permeable board body 2 capable of performing ventilation from a lower section to an upper section is installed onto the external surface of the floor beam 1 of the upper story, and the lower end section of an external facing material 32 in the upper story is abutted against the external surface of the permeable board body 2. A permeable layer 64 mounted inside an external facing material 62 set up on the external surface of a ceiling beam 5 in the lower story is made to communicate with a permeable layer 34 installed inside the external facing material 32 in the upper story through the permeable board body 2.