A sensor insertion device includes a housing, a needle member including a needle portion and movable in the housing in an insertion direction and a pulling-out direction, a first urging member configured to urge the needle member in the insertion direction to move the needle member to a first position at which the needle portion is located in a living body, a second urging member configured to urge the needle member in the pulling-out direction to move the needle member that has reached the first position to a second position at which the needle portion is located out of the living body, and a switching mechanism configured to perform selective switching from movement of the needle member by an urging force of the first urging member to movement of the needle member by an urging force of the second urging member.
