An image forming device includes a main casing and a photosensitive unit. The photosensitive unit has a first peripheral portion at a downstream side in an attaching direction provided with a first contact portion and has a second peripheral portion at an upstream side in the attaching direction provided with a second contact portion. The main casing includes a pair of side walls and first and second positioning members. The first and second positioning members span between the side walls. The first positioning member has a first positioning portion with which the first contact portion is contactable for positioning the photosensitive unit relative to the main casing. The second positioning member is positioned upstream of the first positioning member in the attaching direction. The second positioning member has a second positioning portion with which the second contact portion is contactable for positioning the photosensitive unit relative to the main casing.