Abstract: A ventilator according to the present disclosure includes a first air flow path that draws in indoor air and blows out air into an indoor space, a second air flow path that draws in indoor air and blows out air to an outdoor space, first blower means placed in the first air flow path, second blower means placed in the second air flow path, a desiccant rotor which is placed across the first air flow path and the second air flow path and in which a portion located in the first air flow path and a portion located in the second air flow path are switched over time by rotation, and a first heat exchanger located upstream of the desiccant rotor in the first air flow path.

Abstract: A power transmission system transmits rotative power from a driver pulley to a driven pulley through a toothed belt. The tooth tips (27b) and/or tooth bottoms (27c) of teeth of at least the driven pulley (10) lie in a plane including a central axis l.sub.2 of rotation of the driven pulley and are inclined with respect to the central axis l.sub.2. When the toothed belt (14) is operated to transmit the rotative power, the position where teeth of the pulley (10) and teeth of the toothed belt (14) start meshing with each other is progressively displaced, thus lowering the level of impact sounds produced when the teeth mesh with each other.