This image forming device 1 comprises an image processing unit 9, an HDD 23 and an image forming unit. The image processing unit 9 is capable of instructing the output of the image data sent from the PC 43. The HDD 23 is connected to the image processing unit 9 and is capable of storing the image data to be delivered. The image forming unit is capable of receiving the instruction from the image processing unit 9 and delivering onto paper or the like the image data stored in the HDD 23. Then, when the ID information contained in the image data is detected by the image processing unit 9, writing of image data to the HDD 23 is prohibited.