An indwelling needle assembly (1) for introducing a catheter (3) into a vascular system is disclosed. The indwelling needle assembly is provided with: a needle (5) capable of being slidably fitted in the catheter and insertable into the vascular system a base body (7) fixed to a proximal end of the needle a first sleeve (15) slidably fitted around the base body, which is movable between a first position to expose a distal end of the needle and a second position to conceal the distal end of the needle an elastic body (25) intervening between the base body and the first sleeve so as to urge the first sleeve toward the second position a second sleeve (19) telescopically fitted to the first sleeve, which includes a latching device (31) configured to hold the first sleeve at the second position a cover (17) fixed to the base body, which is so dimensioned as to house the first sleeve and the second sleeve when the first sleeve is at the first position and a lock (39) configured to releasably hold the first sleeve at the first position.
