A printing system comprising: a printing means configured to execute a print job for printing an image on a sheet; a sheet processing means configured to execute a sheet process on the sheet conveyed from the printing means and execute the sheet process on an insert sheet inserted into a sheet insertion slit, which is provided in a front of the sheet processing means; a detection means configured to detect the insert sheet inserted via the sheet insertion slit on which the sheet process is to be executed by the sheet processing means not in association with printing of an image by the printing means; a control means configured to: in a case where the insert sheet is detected by the detection means and in a case where the print job is not executed, set a mode for executing the sheet process on the insert sheet, after setting the mode, upon receiving a user instruction or upon a lapse of a predetermined time, cause the sheet processing means to execute the sheet process on the insert sheet, cancel the setting of the mode if the sheet process is executed on the insert sheet or if the insert sheet is no longer detected by the detection means, wherein the control means is further configured to wait, without starting a print operation of printing an image on a sheet in a print job received during a period in which the mode is set, until setting of the mode is cancelled, and the control means is further configured to start the print operation in the print job received during said period after the wait in response to cancellation of the setting of the mode. a printing means configured to execute a print job for printing an image on a sheet; a sheet processing means configured to execute a sheet process on the sheet conveyed from the printing means and execute the sheet process on an insert sheet inserted into a sheet insertion slit, which is provided in a front of the sheet processing means; a detection means configured to detect the insert sheet inserted via the sheet insertion slit on which the sheet process is to be executed by the sheet processing means not in association with printing of an image by the printing means; a control means configured to: in a case where the insert sheet is detected by the detection means and in a case where the print job is not executed, set a mode for executing the sheet process on the insert sheet, after setting the mode, upon receiving a user instruction or upon a lapse of a predetermined time, cause the sheet processing means to execute the sheet process on the insert sheet, cancel the setting of the mode if the sheet process is executed on the insert sheet or if the insert sheet is no longer detected by the detection means, wherein the control means is further configured to wait, without starting a print operation of printing an image on a sheet in a print job received during a period in which the mode is set, until setting of the mode is cancelled, and the control means is further configured to start the print operation in the print job received during said period after the wait in response to cancellation of the setting of the mode. in a case where the insert sheet is detected by the detection means and in a case where the print job is not executed, set a mode for executing the sheet process on the insert sheet, after setting the mode, upon receiving a user instruction or upon a lapse of a predetermined time, cause the sheet processing means to execute the sheet process on the insert sheet, cancel the setting of the mode if the sheet process is executed on the insert sheet or if the insert sheet is no longer detected by the detection means, wherein the control means is further configured to wait, without starting a print operation of printing an image on a sheet in a print job received during a period in which the mode is set, until setting of the mode is cancelled, and the control means is further configured to start the print operation in the print job received during said period after the wait in response to cancellation of the setting of the mode.