Nagashima has four children. His eldest son, Kazushige Nagashima, is a former professional baseball player, and currently works as a sportscaster. Kazushige was not as successful as his father on the field, but he played on the Yomiuri Giants when his father was manager, and has since launched a successful career as an actor and TV personality. His eldest daughter works as a businesswoman, and his younger daughter was a newscaster for TV Asahi. His youngest son is a professional race-car driver. Kazushige had twin daughters in 2004, making Nagashima a grandfather. Shigeo lost his wife, Akiko, on September 18, 2007.