A technique by which when printing is initiated, printed sheets remaining in a large-volume stacker and sheets printed in a subsequent job are not mixed in the large-volume stacker is provided. A printing system in which a printing apparatus and a post-processing apparatus for receiving a sheet printed by the printing apparatus and performing post-processing are connected, upon activation of the printing system, when detecting that a sheet is stacked in the post-processing apparatus, instructs the processing apparatus to discharge the remaining sheet.