Case. A 54-year old woman was found to have an abnormal shadow in a regular checkup chest X-ray film. We suspected a bronchial artery aneurysm based on a contrast-enhanced chest CT. Aortography, bronchial arteriography and pulmonary arteriography showed a bronchial artery aneurysm, 2 cm in diameter, connecting the right bronchial artery, inferior phrenic artery, and pulmonary artery. Bronchoscopy revealed dilatation and hypervascularity of moniliform submucosal vessels below the right truncus intermedius. She underwent bronchial artery embolization several times, but new feeding vessels developed each time. We considered this case required surgical resection. Bronchoscopy after aneurysmectomy revealed decrease of moniliform submucosal vessels. Histological examination revealed a three-layer structure leading to both the pulmonary and bronchial arteries. Conclusion. We diagnosed idiopathic bronchial artery aneurysm connecting to a pulmonary artery.