After his father Nobushige died in the fourth battle of Kawanakajima in 1561, Nobutoyo took over his father's post and became a territorial lord's relative who become the head of his own family.
永禄4年（1561年）、第4次川中島の戦いにおいて父の信繁が戦死し、信豊は後を継いで親族衆に列する。