In August, 1580, he received a letter of chastisement from Nobunaga consisting of 19 articles, and was banished to Mt. Koya along with his legitimate son Nobuhide SAKUMA.
同年8月、信長から19ヶ条にわたる折檻状を突きつけられ、信盛は嫡男・佐久間信栄と共に高野山に追放された。