The patient was a 51-year-old man who visited the hospital with swelling of the anterior chest. Chest computed tomography detected a tumor developing from the anterior mediastinum to the anterior chest wall. There was weak contrast enhancement inside the tumor, and calcification was observed in the central region. A soft tumor with an obscure border and that adhered to the back of the left sternum was surgically removed with thymic fat including the region of the chest wall that had been penetrated by the tumor. The tumor measured 30 x 25 mm, and a phlebolith was observed in the center. The pathological tissue was diagnosed to be a cavernous hemangioma, and there were no malignant findings in the endothelial cells. Mediastinal hemangioma should therefore be kept in mind during an evaluation of mediastinal tumors, and one must also take into account the effect on the surrounding organs.