To provide an image forming device in which thin lines and isolated points can be favorably reproduced even in the case where a positive electrification type photosensitive drum and positive electrification type toner are used.

Using a positive chargeability type photosensitive drum 20 and positive chargeability type toner 53, a developing roller 56 is pressed to the photosensitive drum 20 for impression development. Developer is composed to be provided with styrene acryl toner, and charge control agent comprising at least either of nigrosine and triphenyl methane, and fourth grade ammonium salt. As a result, charging amount of the toner 53 after passing a nip part of the photosensitive drum 20 and the developing roller 56 becomes larger than charging amount of the toner 53 on the developing roller 56 before passing the nip part, and excessive reduction of a potential at a white surface part is prevented, so that potential at the white surface part and a development bias potential are kept proper. Thin lines and isolated points can thus be favorably reproduced, and generation of fogging can be prevented.