A sensor insertion device includes: a housing； a needle member comprising a needle portion configured to be inserted in the living body with a sensor and to be 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； 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； 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 when the needle member reaches the first position.
