To economically perform energy saving in accompany with ventilation in a wider range of a building.

In this building having a living room 1 and a corridor 3 adjacent to the living room 1, and provided with an air heat exchanger 4 exchanging heat between supply air and exhaust air in accompany with the ventilation while ventilating the living room 1, an exhaust opening 8 is formed to exhaust the air in the corridor 3 to the external of the building, and an indoor air supply opening 6b in an exhaust flow channel of the air heat exchanger 4 is formed in a state of being opened to the corridor 3.