A printing apparatus according to this invention includes a plurality of paper feed cassettes. Upon receiving a print job which designates a paper feed cassette, the printing apparatus determines whether the paper size of the paper feed cassette designated by the print job that is stored in a memory matches the paper size needed for executing the print job. If the printing apparatus determines that these paper sizes do not match each other, it restricts execution of the print job. If a feeding unit is set while execution of the print job is restricted, the printing apparatus decides the set feeding unit as a feeding source of paper used to execute the print job. The printing apparatus feeds paper contained in the decided feeding unit, and executes the print job.