member of the Japan Self-Defense Forces
Refers to an individual serving in the Japan Self-Defense Forces (JSDF).
He participated in disaster relief as a member of the Self-Defense Forces.
自衛官 specifically means a uniformed service member, whereas 自衛隊員 is a broader term that also includes civilian staff working for the organization.
Compound of 自衛 (self-defense) + 隊 (corps, unit) + 員 (member).