A negative-ion source comprising means for discharging alkaline metal for discharging neutral alkaline metal particles together with alkaline metal ion particles; an electrode for generating negative ions which can serve as an extraction electrode for extracting said alkaline metal ion particles and a target bombarded with said alkaline metal ion particles and which provides with a hold for holding negative-ion seed material in the portion bombarded with said alkaline metal ion particles and an aperture for letting out negative-ion particles; and a negative-ion extraction electrode for said negative-ion particles. The present negative-ion source has an improved ion current efficiency and is compact size.