An image processing device comprising: operating units (21,35-39) including a printing unit for forming an image on a recording sheet, the printing unit including a sheet-conveying mechanism and a fixing unit; a plurality of control units (31,32) each including a processing unit (31A,32A) and being configured to control the printing unit to form an image on a recording sheet, the plurality of control units (31,32) including at least a first control unit and a second control unit; and a selecting unit that is configured to select one of a high-speed mode and a power-saving mode, wherein: when the high-speed mode is selected, the plurality of control units (31,32) are configured to control, in cooperation with each other, the printing unit to form the image on the recording sheet and to control the sheet-conveying mechanism to convey the recording sheet at a first feeding speed; and when the power-saving mode is selected, the second control unit is configured to control, by itself without cooperating with the first control unit, the printing unit to form the image on the recording sheet and to control the sheet-conveying mechanism to convey the recording sheet at a second feeding speed lower than the first feeding speed, enabling the fixing unit to thermally fix toner images onto the recording sheet at a lower temperature. operating units (21,35-39) including a printing unit for forming an image on a recording sheet, the printing unit including a sheet-conveying mechanism and a fixing unit; a plurality of control units (31,32) each including a processing unit (31A,32A) and being configured to control the printing unit to form an image on a recording sheet, the plurality of control units (31,32) including at least a first control unit and a second control unit; and a selecting unit that is configured to select one of a high-speed mode and a power-saving mode, wherein: when the high-speed mode is selected, the plurality of control units (31,32) are configured to control, in cooperation with each other, the printing unit to form the image on the recording sheet and to control the sheet-conveying mechanism to convey the recording sheet at a first feeding speed; and when the power-saving mode is selected, the second control unit is configured to control, by itself without cooperating with the first control unit, the printing unit to form the image on the recording sheet and to control the sheet-conveying mechanism to convey the recording sheet at a second feeding speed lower than the first feeding speed, enabling the fixing unit to thermally fix toner images onto the recording sheet at a lower temperature. when the high-speed mode is selected, the plurality of control units (31,32) are configured to control, in cooperation with each other, the printing unit to form the image on the recording sheet and to control the sheet-conveying mechanism to convey the recording sheet at a first feeding speed; and when the power-saving mode is selected, the second control unit is configured to control, by itself without cooperating with the first control unit, the printing unit to form the image on the recording sheet and to control the sheet-conveying mechanism to convey the recording sheet at a second feeding speed lower than the first feeding speed, enabling the fixing unit to thermally fix toner images onto the recording sheet at a lower temperature.