An image forming apparatus, comprising: a controller comprising: an image processing unit to prepare page-by-page image drawing data by converting image data input to the image forming apparatus; a data storage unit to store the image drawing data prepared by the image processing unit; and a page-number obtaining unit to obtain the total number of pages of the image drawing data stored in the data storage unit; and an image forming unit configured to output an image on a recording medium based on the image drawing data, wherein the image forming unit comprises one or more devices (33, 34) used for an image forming process; characterized in that: the controller further comprising: a data management unit to output the total number of pages and the image drawing data stored in the data storage unit to the image forming unit; and an interface configured to transmit the image drawing data and the total number of print pages of the image drawing data to the image forming unit; the image forming unit further comprising: a power saving unit configured to shift the image forming apparatus to a reduced-power mode that reduces power supply to the one or more devices (33, 34) used for an image forming process upon completing output of an image of the last page of the image drawing data, wherein the image forming unit manages the number of image forming pages based on the total number of pages received from the data management unit. a controller comprising: an image processing unit to prepare page-by-page image drawing data by converting image data input to the image forming apparatus; a data storage unit to store the image drawing data prepared by the image processing unit; and a page-number obtaining unit to obtain the total number of pages of the image drawing data stored in the data storage unit; and an image processing unit to prepare page-by-page image drawing data by converting image data input to the image forming apparatus; a data storage unit to store the image drawing data prepared by the image processing unit; and a page-number obtaining unit to obtain the total number of pages of the image drawing data stored in the data storage unit; and an image forming unit configured to output an image on a recording medium based on the image drawing data, wherein the image forming unit comprises one or more devices (33, 34) used for an image forming process; wherein the image forming unit comprises one or more devices (33, 34) used for an image forming process; characterized in that: the controller further comprising: a data management unit to output the total number of pages and the image drawing data stored in the data storage unit to the image forming unit; and an interface configured to transmit the image drawing data and the total number of print pages of the image drawing data to the image forming unit; the image forming unit further comprising: a power saving unit configured to shift the image forming apparatus to a reduced-power mode that reduces power supply to the one or more devices (33, 34) used for an image forming process upon completing output of an image of the last page of the image drawing data, wherein the image forming unit manages the number of image forming pages based on the total number of pages received from the data management unit. the controller further comprising: a data management unit to output the total number of pages and the image drawing data stored in the data storage unit to the image forming unit; and an interface configured to transmit the image drawing data and the total number of print pages of the image drawing data to the image forming unit; a data management unit to output the total number of pages and the image drawing data stored in the data storage unit to the image forming unit; and an interface configured to transmit the image drawing data and the total number of print pages of the image drawing data to the image forming unit; the image forming unit further comprising: a power saving unit configured to shift the image forming apparatus to a reduced-power mode that reduces power supply to the one or more devices (33, 34) used for an image forming process upon completing output of an image of the last page of the image drawing data, wherein the image forming unit manages the number of image forming pages based on the total number of pages received from the data management unit. a power saving unit configured to shift the image forming apparatus to a reduced-power mode that reduces power supply to the one or more devices (33, 34) used for an image forming process upon completing output of an image of the last page of the image drawing data, wherein the image forming unit manages the number of image forming pages based on the total number of pages received from the data management unit.