A printing system, comprising: a reader unit for reading an original document and generating image data; a printer unit for performing a. printing process on a sheet based on the image data generated by the reader unit; a bookbinding unit for performing a case binding process which includes gluing of a spine of a sheet bundle on which the printing process has been performed and casing with a cover sheet the sheet bundle on which the gluing has been performed; a conveying unit capable of conveying the sheet from the printer unit to the bookbinding unit; and a display unit for displaying a setting screen for a user to set a page layout condition; characterized by a CPU circuit unit for calculating, before the printer unit starts the printing process, a number of sheets to be used as body sheets of the case binding process, based on a number of the original documents read by the reader unit and the page layout condition set on the setting screen, wherein the CPU circuit unit permits the printing unit to start the printing process in a case where the number of the sheets calculated by the CPU circuit unit is greater than or equal to a first number indicating a lower limit of sheets appropriate for the case binding process and is less than or equal to a second number indicating an upper limit of sheets appropriate for the case binding process, and the CPU circuit unit inhibits the printing unit from starting the printing process in a case where the number of the sheets calculated by the CPU circuit unit is less than the first number or is greater than the second number, the printer unit being capable of performing a printing process of data of a plurality of jobs stored in a storage unit. a reader unit for reading an original document and generating image data; a printer unit for performing a. printing process on a sheet based on the image data generated by the reader unit; a bookbinding unit for performing a case binding process which includes gluing of a spine of a sheet bundle on which the printing process has been performed and casing with a cover sheet the sheet bundle on which the gluing has been performed; a conveying unit capable of conveying the sheet from the printer unit to the bookbinding unit; and a display unit for displaying a setting screen for a user to set a page layout condition; characterized by a CPU circuit unit for calculating, before the printer unit starts the printing process, a number of sheets to be used as body sheets of the case binding process, based on a number of the original documents read by the reader unit and the page layout condition set on the setting screen, wherein the CPU circuit unit permits the printing unit to start the printing process in a case where the number of the sheets calculated by the CPU circuit unit is greater than or equal to a first number indicating a lower limit of sheets appropriate for the case binding process and is less than or equal to a second number indicating an upper limit of sheets appropriate for the case binding process, and the CPU circuit unit inhibits the printing unit from starting the printing process in a case where the number of the sheets calculated by the CPU circuit unit is less than the first number or is greater than the second number, the printer unit being capable of performing a printing process of data of a plurality of jobs stored in a storage unit.