On a production line for component mounting substrate, mutually communicating inspection apparatus are each provided to a different one of production processes that are carried out sequentially such as the solder printing, component mounting and soldering processes. Each inspection apparatus can generate an X-ray transmission image of the substrate. Each inspection apparatus on the downstream side inputs an image from another inspection apparatus on the upstream side and generates a differential image of the inputted image and an X-ray transmission image of the same substrate generated by itself after the production process associated with itself is carried out. The differential image thus generated is used for inspecting the substrate such that the effect of the associated production process can be more accurately inspected.