A sensor insertion device for inserting a detection element of a sensor measuring biological information of a subject into the body of the subject, the sensor insertion device comprising: a device body to which a data process unit processing a signal including biological information detected by the detection element is attached; a movement mechanism detachably attached to the device body, the movement mechanism moving the detection element together with an insertion needle to be stuck into the body of the subject to insert the detection element and the insertion needle into the body of the subject; a displacement preventing member prevent displacement of the movement mechanism toward the body of the subject; the movement mechanism including a hollow guide member engageable with the device body, a needle holding member pushing the insertion needle to move inside the guide member, a grip member gripped by an operator, a pushing member held by the grip member and displaced to push the needle holding member interlocking with displacement of the grip member along the guide member caused by the operator, and a resilient member elastically biasing the needle holding member in a direction away from the device body; and a displacement preventing member preventing displacement of the movement mechanism toward the body of the subject, wherein the displacement preventing member blocks the grip member when the data process unit is not attached to the device body and, on the other hand, moves under a pushing action of the data process unit to release the blockage with respect to the grip member when the data process unit is attached to the device body, the insertion needle is stuck into the body of the subject when the pushing member is displaced along with displacement of the grip member released from the blockage by the displacement preventing member toward the body of the subject and the pushing member pushes the needle holding member, the pushing member remaining held by the grip member is engaged with the guide member when the pushing member reaches a displacement end point, the guide member is released from engagement with the device body by the grip member when the grip member and the pushing member reach the displacement end point, and the needle holding member is displaced in a direction away from the device body by an action of the resilient member when the grip member and the pushing member reach the displacement end point, so that the detection element is implanted inside the body by the engagement between the pushing member and the guide member, the release of the engagement of the guide member with the device body, and the displacement of the needle holding member in the direction away from the device body. a device body to which a data process unit processing a signal including biological information detected by the detection element is attached; a movement mechanism detachably attached to the device body, the movement mechanism moving the detection element together with an insertion needle to be stuck into the body of the subject to insert the detection element and the insertion needle into the body of the subject; a displacement preventing member prevent displacement of the movement mechanism toward the body of the subject; the movement mechanism including a hollow guide member engageable with the device body, a needle holding member pushing the insertion needle to move inside the guide member, a grip member gripped by an operator, a pushing member held by the grip member and displaced to push the needle holding member interlocking with displacement of the grip member along the guide member caused by the operator, and a resilient member elastically biasing the needle holding member in a direction away from the device body; and a displacement preventing member preventing displacement of the movement mechanism toward the body of the subject, wherein the displacement preventing member blocks the grip member when the data process unit is not attached to the device body and, on the other hand, moves under a pushing action of the data process unit to release the blockage with respect to the grip member when the data process unit is attached to the device body, the insertion needle is stuck into the body of the subject when the pushing member is displaced along with displacement of the grip member released from the blockage by the displacement preventing member toward the body of the subject and the pushing member pushes the needle holding member, the pushing member remaining held by the grip member is engaged with the guide member when the pushing member reaches a displacement end point, the guide member is released from engagement with the device body by the grip member when the grip member and the pushing member reach the displacement end point, and the needle holding member is displaced in a direction away from the device body by an action of the resilient member when the grip member and the pushing member reach the displacement end point, so that the detection element is implanted inside the body by the engagement between the pushing member and the guide member, the release of the engagement of the guide member with the device body, and the displacement of the needle holding member in the direction away from the device body.