Ventilating and air purifying device including a case having a blower therein provided to a ceiling or a wall, a first flow passage provided between the blower and a room for making an outdoor, the blower, and the room in communication, a second flow passage for making the room, an inside of the case, and the outdoor in communication, and a damper in the case for isolating the first flow passage from the second flow passage so that room air is discharged to the outdoor and the room air is guided to the blower, or making the first flow passage and the second flow passage in communication so that the room air introduced into the second flow passage is guided to the blower, thereby ventilating and purifying the room air.