The sensor insertion device and the sensor insertion device set according to the present invention include a housing, a needle portion, a needle member that can move in the housing in the insertion direction and the removal direction, and urge the needle member in the insertion direction. Then, the first biasing member that moves the needle member to a first position where the needle portion can be inserted into the living body, and the needle member that biases the needle member in the removal direction, A second urging member that moves the needle portion that has reached the first position to a second position where the needle portion can be removed from the living body； and when the needle member reaches the first position, the first portion A switching mechanism capable of selectively switching from movement of the needle member by the biasing force of the biasing member to movement of the needle member by the biasing force of the second biasing member.本発明に係るセンサ挿入装置及びセンサ挿入装置セットは、ハウジングと、針部を有し、挿入方向及び抜去方向に前記ハウジング内を移動可能な針部材と、前記針部材を前記挿入方向に付勢して、前記針部材を、前記針部が生体内へ挿入可能な第１の位置まで移動させる第１付勢部材と、前記針部材を前記抜去方向に付勢して、前記針部材を、前記第１の位置に到達した前記針部が生体内から抜去可能な第２の位置まで移動させる第２付勢部材と、前記針部材が前記第１の位置に到達した際に、前記第１付勢部材の付勢力による前記針部材の移動から、前記第２付勢部材の付勢力による前記針部材の移動へと択一的に切り替え可能な切り替え機構と、を備える。
