To prevent clogging and freezing of a filter by snow in an outside air introduction circuit, and generation of vapor in an air conditioner by optimally controlling temperature/humidity in an air-conditioned room.

This outside air-cooling air conditioning system includes an air supply flow channel and an air return flow channel, the outside air introduction circuit, and an exhaust flow channel and a recirculation flow channel. A vaporization type humidifier and a cold water coil at a downstream side of the humidifier are disposed in the recirculation flow channel, a first bypass circuit and a first electric damper are disposed for connecting the upstream side and the downstream side of the vaporization type humidifier, a second bypass circuit and a second electric damper are disposed for connecting the downstream side of the vaporization type humidifier and the outside air introduction circuit, and a third bypass circuit and a third electric damper are disposed for connecting the upstream side of the vaporization type humidifier and the outside air introduction circuit. A snow sensor is disposed near an outside air inlet of the outside air introduction circuit. A humidification amount supplied to the air-conditioned room is controlled by the first electric damper, and the outside air introduction circuit is controlled by the second electric damper when intrusion of snow is detected by the snow sensor.