To provide an image forming device having improved user-friendliness while preventing the entry of foreign matters including dirt and dust into a supply port of recording media.

The image forming device 1 which has the supply port 25 into which a recording medium packing material 30 is mounted for packing stacked recording media P forms images on the recording media P supplied from the recording medium packing material 30 to an image forming part 5 in the state in which the recording medium packing material 30 is mounted into the supply port 25. The recording medium packing material 30 has a body 31 for storing the recording media P and a cover portion 32 to be separated from the body 31 in the state of being partially connected to the body 31. A locking portion S locks the cover portion 25 so that the supply port 25 is covered with the cover portion 32 separated form the body 31 when the recording medium packing material 30 is mounted into the supply port 25.