Provided are an injection needle assembly and a mene injection device capable of preventing accidental puncture of a needle point of a needle tube after administration or disposal of a mene. The needle assembly (2) of the present invention comprises a needle tube (21), a needle hub (22) for holding a needle tube (21), a protector (26) provided with an abutment piece (29) The protector (26) includes a member (27), a retaining member (43), and a holding and releasing mechanism (41, 42). The protector (26) has a first position to expose the needle tip (21 a) of the needle tube (21) of the needle tube (21), and the urging member (27) can move the protector (26) in the axial direction of the needle tube (21) in the axial direction of the needle tube (43) urges the contact piece (29) from the first position toward the second position, and the retaining member (43) contacts the contact piece (29) when the protector (26) moves to the second position. Then, the holding and releasing mechanism (41, 42) detachably holds the protector (26) in the first position.薬剤の投与後や廃棄時に針管の針先が誤って使用者に穿刺されることを防止できる注射針組立体及び薬剤注射装置を提供する。 本発明の注射針組立体(2)は、針管(21)と、針管(21)を保持する針ハブ(22)と、当接片(29)が設けられたプロテクタ(26)と、付勢部材(27)と、抜け止め部材(43)と、保持及び解除機構(41,42)とを備え、プロテクタ(26)は、針管(21)の針先(21a)を露出させる第1の位置と、針管(21)の針先(21a)を覆う第2の位置に移動可能となっており、付勢部材(27)は、プロテクタ(26)を針管(21)の軸方向に沿って、第1の位置から第2の位置に向けて付勢し、抜け止め部材(43)は、プロテクタ(26)が第2の位置に移動した際に、当接片(29)と当接する。そして、保持及び解除機構(41,42)は、プロテクタ(26)を第1の位置に着脱可能に保持する。
