It is possible to avoid increasing the size of the outer needle hub toward the outer periphery side while maintaining the protection mechanism of the needle tip of the inner needle withdrawn from the outer needle, An indwelling needle assembly of a novel structure is provided. In the indwelling needle assembly 10, the needle tip protector 22 extends from the needle tip protector 22 to the inside of the outer needle hub 26, abuts against the inner surface of the outer needle hub 26, regulates the relative movement of the outer needle hub 26 with respect to the needlepoint protector 22, The connecting member 94 maintaining the connected state by the mechanism is provided and at the time of withdrawing the inner needle 18 from the outer needle 24, the connecting member 94 is moved to the inner peripheral side of the outer needle hub 26 and the needle tip protector 22 of the outer needle hub 26 In order to release the connection state to the other end.外針から引き抜かれた内針の針先の保護機構を維持しつつ、外針ハブの外周側へのサイズの大型化を回避することが可能とされて、施術に際しての作業も容易となる、新規な構造の留置針組立体を提供する。 留置針組立体10において、針先プロテクタ22から外針ハブ26の内側に延び出し、外針ハブ26の内面に当接して外針ハブ26の針先プロテクタ22に対する相対移動を規制することで連結機構による連結状態を維持する連結部材94を設けると共に、内針18の外針24からの引抜きに際して連結部材94を外針ハブ26の内周側へ移動させて外針ハブ26の針先プロテクタ22への連結状態を解除する連結解除機構を設けた。
