Abstract: To determine whether chip components are properly mounted on a printed circuit board, two sets of slit light beams for projecting slit line images in mutually perpendicular directions are alternately made incident thereon diagonally from above. Edges of the mounted chip components produce discontinuities in the projected slit beam image patterns such that the positions, sizes, orientations, etc. of individual mounted components can be calculated from image data obtained from viewing positions above the circuit board by a camera or the like. Since it can be easily ascertained how the slit line image pattern should appear if proper components are properly mounted, an analysis of the calculated data can indicate whether the chip components are properly mounted on the tested printed circuit board.