PURPOSE: To adjust a back focus while maintaining the parallelism of a solid- state image pickup element to a lens surface by constituting freely slidably a cylindrical holder.

CONSTITUTION: A lens 1 is mounted on a camera body which is not shown in a figure through a dedicated mount 10, the cylindrical holder 11 is arranged in the dedicated mount 10, and an optical filter 2 and the solid-state image pckup element 4 are fitted to the holder 11 in parallel. When the focus is adjusted, a fixing screw 12 is loosened and the holder 11 is moved to attain the adjustment, but the parallilism between the optical filter 2 and solid-state image pickup element 4, and lens surface 9 is always held without fail.