To provide a cereal grain storage box that has a simple constitution and can automatically maintain appropriate humidity in the box.

This cereal grain storage box having a ventilation system equipped is equipped with a humidity detector near the ventilating opening and a ventilation operation-controlling means so that the controlling means may control the ventilation unit on the basis of the outside air humidities and the inside air humidity detected by the detector, when the ventilation unit stops and starts operating. In the case where the outside air humidity is lower than that inside the storage box, the ventilation unit is operated by the ventilation operation controlling means.