The present invention provides an in-line printing system including a printing apparatus and an inspection apparatus for inspecting a product outputted by the printing apparatus. In addition, the printing apparatus sequentially assigns page information to each page of the product outputted by the printing module, assigns additional information indicating an additional page inserted by the printing module, and sequentially notifies the inspection apparatus of the page information and the additional information. The inspection apparatus receives the notified page information and additional information, compares the page information and the additional information, and performs inspection by comparing a printed material according to the inspection job excluding the additional page from the product based on a comparison result and pre-registered correct images corresponding to respective pages of the printed material.