Has an outer needle, a flow passage communicating with the outer needle in the indwelling needle is provided which can be connected with the outer needle hub, and a valve mechanism for blocking and opening the flow path in the connector passage. Includes a valve body having an openable closing portion provided in the middle of the passage, made of an elastic material, and an operating member having a side hole and opening and closing the closing part, the valve mechanism, operation member may take the state where projects side hole is positioned at the front end side from the switching unit switching unit through the switching unit. In this state, when the infusion solution is supplied from the connector, infusion solution flows out into the flow path through the side holes, a dead space in the flow path is replaced with infusate which flows out through the side hole .留置針は、外針と、外針内と連通する流路を有し、流路にコネクタを接続可能な外針ハブと、流路を遮断・開放する弁機構とを備えている。弁機構は、流路の途中に設けられ、弾性材料で構成された開閉可能な開閉部を有する弁体と、側孔を有し、開閉部を開閉操作する操作部材とを備え、操作部材が開閉部を貫通して開閉部から突出し、側孔が開閉部よりも先端側に位置する状態を取り得る。この状態で、コネクタから輸液剤が供給された際、輸液剤が側孔を介して流路に流出し、その流路のデッドスペースが、前記側孔を介して流出した輸液剤で置換される。
