A needle assembly 1 includes a hub 4 retaining a cannula3, a protective unit 5 advancing and retracting to surroundthe forward end of the cannula 3, and a cylindrical portion6 surrounding the outer periphery of the protective unit 5；the protective unit 5 has a construction in which a protectivecover 7 protruding from and retracting into the cylindricalportion 6 is formed integrally with a spring portion 8 so asto be in series therewith, with the hub 4 and the cylindricalportion 6 being coupled together to form a hub member.Further, the protective cover 7 is provided with anengagement protrusion 24, and the hub member is provided witha guide means G； when the protective cover 7 is retracted froma pre-use state (Fig. 4(a)) in which it is situated at anadvanced position, the engagement protrusion 24 movesbackwards while rotating and in contact with an inclinedsurface 14a (Fig. 4(b))； when the protective cover 7 advancesfrom a use state (Fig. 4(c)) in which it is situated at aretracted position, the engagement protrusion 24 movesforwards to be fixed to a post-use retaining portion B to bethereby prevented from retracting.The needle assembly can be produced at low cost and usedsafely.
