Provided is an image forming system operable to provide a cloud printing service, the image forming system comprising: a transmitting device operable to transmit content by designating a target phone number; a cloud printing server operable to receive the target phone number and the content from the transmitting device; a receiving device assigned with the target phone number and operable to receive an upload notification of the content with respect to the target phone number from the cloud printing server; and an image forming device operable to print the content by receiving the content from the cloud printing server, wherein the cloud printing server transmits the content to the image forming device registered in the target phone number when the cloud printing service is requested for the content to the target phone number.