The columnar sections (56) of a cover (48) constituting a needle cover (34) have engagement sections (62) formed on the columnar sections (56) so as to protrude therefrom. The engagement sections (62) engage with the stopper wall (70) of an outer cylinder (32) to prevent the needle cover (34) from dislodging from the outer cylinder (32) . An inner cylinder (30) pressed toward a barrel (12) by a spring member (36) is accommodated within the outer cylinder (32), that is, within a through-hole (64). The needle cover (34) is interconnected with the inner cylinder (30). The cam protrusions (42a, 42b) of the inner cylinder (30) movably engage with guide passages (72a, 72b) formed in the outer cylinder (32) to retain the inner cylinder (30) within the outer cylinder (32).
