A liquid injection instrument 1 includes: an outer cylinder 3 having a liquid receiving space 33 a liquid introduction section 4 formed at a front portion of the outer cylinder 3 and having a flow passage 41 formed therein communicating with the liquid receiving space 33 an inside plug 7 configured to be displaceable with respect to the liquid introduction section 4 and communicate with the flow passage 41, and having a liquid introduction passage 75 which can allow the flow passage 41 to be opened, the inside plug 7 being displaced between a first position where the flow passage 41 and the liquid introduction passage 75 are cut-off from each other, and a second position where the flow passage 41 and the liquid introduction passage 75 are communicated with each other a hub 11 mounted on the inner plug 7, a needle pipe 12 supported in the hub 11 and communicating with the flow passage 41 via the liquid introduction passage 75 when the inside plug 7 is located at the second position, and a protector 9 covering the needle pipe 12 in a mounting state in which the protector 9 is fixed to the inside plug 7, wherein the inside plug 7 is displaced from the first position to the second position accompanied with a detaching operation of the protector 9 for exposing the needle pipe 12.本發明之液體注入器具(1)係具備:外筒(3),具有液體收納空間(33);導液部(4),形成於外筒(3)之前端部,且於內部具有連通至液體收納空間(33)的流路(41);內栓(7),以能夠相對於導液部(4)位移的方式設置,具有與流路(41)連通、並可開放流路(41)的導液路(75),且能夠位移至流路(41)和導液路(75)被切斷的第1位置、及流路(41)與導液路(75)連通的第2位置;轂部(11),裝配於內栓(7);針管(12),由轂部(11)所支撐,且在內栓(7)位於第2位置時透過導液路(75)而與流路(41)連通;以及保護器(9),在固定於內栓(7)之裝配狀態下覆蓋針管(12);而內栓(7)係伴隨使針管(12)露出的保護器(9)之脫離操作,從第1位置位移至第2位置。1‧‧‧液體注入器具2‧‧‧液體注入器具本體3‧‧‧外筒(注射器外筒)4‧‧‧導液部7‧‧‧內栓9‧‧‧保護器(蓋)10‧‧‧注射針11‧‧‧轂部(針轂部)12‧‧‧針管20‧‧‧轉動限制手段30‧‧‧脫離防止手段31‧‧‧底部32、95、113‧‧‧凸緣33‧‧‧液體收納空間34‧‧‧段差部(擋止部)42‧‧‧側孔43‧‧‧凹部44‧‧‧外周部(側面)71‧‧‧內栓本體72‧‧‧外側環75‧‧‧導液路77‧‧‧爪部(突部)91‧‧‧保護器本體92‧‧‧裝配部93‧‧‧破斷部96‧‧‧腳部98‧‧‧開縫99‧‧‧凸部111‧‧‧內腔部114、712‧‧‧外周部122‧‧‧針頭713‧‧‧前端面751‧‧‧橫向孔(貫通孔)752‧‧‧縱向槽911‧‧‧前端
