A needle assembly 10 includes a needle hole 16 having an inside diameter that is greater than an outside diameter of a needle 12, and by a moving-side guide 64 integrally provided to a needle tip cover 18 being engaged with a fixed-side guide 30 fixedly provided to the needle 12, a guide mechanism is provided to guide the needle tip cover 18 from a proximal end side towards a distal end side of the needle 12 while maintaining a state of noncontact with the needle 12, and to guide the needle tip cover 18 to a position where the needle tip cover 18 covers the needle tip 20 while deviating the needle tip cover 18 in a direction in which the needle hole 16 goes away from a center axis 102 of the needle 12 at a position beyond the needle tip 20, and avoiding contact of the needle tip 20 with the needle hole 16.
