Silicon nanosized linear bodies with different structures and properties can be produced by appropriately setting the condition for the pretreatment by a radical (reaction condition of a hydrogen radical, e.g. concentration). A silicon nanosized linear body is produced from a silicon radical active species in the presence of a catalyst. The catalyst is at least one selected from Ga, Ga compound, In, In compound, Tl and Tl compound that are pretreated by a radical.