A printing apparatus capable of reducing the frequency of detection of a recording agent remaining amount and obtaining accurate information of the recording agent remaining amount. When a printed sheet is discharged, a CPU of a printer updates information representing the number of discharged sheets and stores the information into a memory of a print engine. The CPU refers to toner remaining amount information stored in a memory of a cartridge and determines whether there is a sufficient toner remaining amount in the cartridge. If there is no sufficient toner remaining amount, toner remaining amount detection is executed each time printing of one page has been performed. If there is a sufficient toner remaining amount, the toner remaining amount detection is executed when the number of discharged sheets coincides with a predetermined value.