A capping system includes: a moving portion moving a stem, on which an optical semiconductor element is mounted, horizontally; a fixer fixing a cap having a window, on the stem; a camera taking an image of the cap and the stem from above the cap and the stem; a detector detecting whether the optical semiconductor element is present within a visual field of the camera; and a searching action controller controlling the moving portion to move the stem so the detector searches the optical semiconductor element. The searching action controller causes searching radially and outwardly from a search starting point.