A 58-year-old man presented with a nodule in the right lung. Initially, the chest CT showed a ground-glass shadow. However, the shadow had become a solid nodule one month later. Histological examination revealed it was an inflammatory pseudotumor of the lung and subsequent surgery showed it to be an organizing pneumonia type. This disease is rare and in most cases is considered to be slow growing. Chest CT findings in the early stages have not been reported previously. Therefore, the present case is noteworthy in that we could confirm the CT findings in the early stages of this disease with rapid growth.