An image forming apparatus capable of preventing unauthorized printing while reducing manager's work load. IP addresses of host computers for which printing should be permitted are registered beforehand in a print permission list. When a print job is received, whether the IP address of a host computer from which the print job has been transmitted is present in the list is determined. If the IP address is not present, the received print job is not printed but stored. Subsequently, when the print job is selected and a print instruction is given, printing is executed. If the print instruction has once been given to the stored print job, the IP address of the host computer is added to the list. Subsequently, printing is executed without any print instruction when a print job is transmitted.