A sensor insertion device for inserting a needle member, together with a sensor configured to detect biological information, into a living body, and for removing the needle member from the living body after leaving a distal end side of the sensor in the living body, the sensor insertion device comprising: an elastic energy variable mechanism; a first elastic member configured to accumulate first elastic energy to move the sensor and the needle member in an insertion direction to an insertion position where the sensor and the needle member are inserted into the living body; a second elastic member configured to accumulate second elastic energy to move the needle member in a removal direction from the insertion position to a removal position where the needle member is removed from the living body; a first holding mechanism configured to hold a position of the first elastic member in the energy accumulated state; and a second holding mechanism configured to hold a position of the second elastic member in the energy accumulated state and for a period of time during which, after the release of the first elastic member from the first holding mechanism in the energy accumulated state, the needle member is moved to the insertion position by the first elastic energy, wherein the elastic energy variable mechanism comprises a fixed member and a movable member that is movable with respect to the fixed member, the fixed member and the movable member sandwiching the first elastic member and the second elastic member therebetween, wherein the elastic energy variable mechanism is configured to elastically deform the first elastic member and the second elastic member by compressive deformation to achieve an energy accumulated state in which the first elastic energy is accumulated in the first elastic member and the second elastic energy is accumulated in the second elastic member, wherein the fixed member comprises a movement restriction portion that is positioned on a removal direction side of the needle member with respect to the first elastic member and the second elastic member, the movable member comprises a main body portion that is positioned on an insertion direction side of the needle member with respect to the first elastic member and the second elastic member, and the main body portion is movable in the removal direction to elastically deform the first elastic member and the second elastic member at the same time between the main body portion and the movement restriction portion, to thereby achieve the energy accumulated state. an elastic energy variable mechanism; a first elastic member configured to accumulate first elastic energy to move the sensor and the needle member in an insertion direction to an insertion position where the sensor and the needle member are inserted into the living body; a second elastic member configured to accumulate second elastic energy to move the needle member in a removal direction from the insertion position to a removal position where the needle member is removed from the living body; a first holding mechanism configured to hold a position of the first elastic member in the energy accumulated state; and a second holding mechanism configured to hold a position of the second elastic member in the energy accumulated state and for a period of time during which, after the release of the first elastic member from the first holding mechanism in the energy accumulated state, the needle member is moved to the insertion position by the first elastic energy, wherein the elastic energy variable mechanism comprises a fixed member and a movable member that is movable with respect to the fixed member, the fixed member and the movable member sandwiching the first elastic member and the second elastic member therebetween, wherein the elastic energy variable mechanism is configured to elastically deform the first elastic member and the second elastic member by compressive deformation to achieve an energy accumulated state in which the first elastic energy is accumulated in the first elastic member and the second elastic energy is accumulated in the second elastic member, wherein the fixed member comprises a movement restriction portion that is positioned on a removal direction side of the needle member with respect to the first elastic member and the second elastic member, the movable member comprises a main body portion that is positioned on an insertion direction side of the needle member with respect to the first elastic member and the second elastic member, and the main body portion is movable in the removal direction to elastically deform the first elastic member and the second elastic member at the same time between the main body portion and the movement restriction portion, to thereby achieve the energy accumulated state.