An image forming device comprises a process cartridge. The process cartridge comprises a development roller. The development roller comprises a magnet roller and a developing sleeve 132. The magnet roller is fixed. The depressions 139 each having an oval shape are formed on the external surface of the developing sleeve 132. Both ends of the depressions 139 which are adjacent with each other along the longitudinal direction of the developing sleeve 132 are overlapped with each other and both ends of the depressions 139 which are adjacent with each other along the circumferential direction of the developing sleeve 132 are spaced with each other.