In July 1621, he was adopted by Yoshinobu SATAKE(Ukyo no daibu) (Master of the Western Capital Offices), his eldest brother and the lord of Kubota Domain, Dewa Province.
元和(日本)7年（1621年）7月、長兄で出羽国久保田藩主の佐竹義宣(右京大夫)の養子になる。