A method includes: providing an assembly including: an inner needle, an inner needle hub, a catheter, a catheter hub, a catheter operating member, and a support member； puncturing a blood vessel of a patient with the inner needle and the catheter, while the support member is at a first position in which the support member supports the catheter； advancing the catheter operation member relative to the needle hub such that the catheter advances in the blood vessel, such that the support member is caused to move from the first position to a second position in which the support member does not support the catheter, and such that the catheter hub detaches from the needle hub； and retracting the inner needle hub and the inner needle relative to the catheter hub and the catheter, while maintaining the catheter in the blood vessel.
