Abstract: A page printer having a housing body and including a gate roller, a developing unit, a photosensitive drum unit, a fixing unit and a sheet discharging roller arranged on the front side of the housing body in the order stated from above so that the printing sheet conveying path is substantially vertical to reduce floor area required for installation. An optical writing unit is provided on the rear side of the housing body. Guide members are provided on the housing body to readily mount or demount the photo-sensitive drum unit. Further, a shield board is disposed between the photo-sensitive drum unit and the fixing unit so that the printing sheet will not be stained by toner scattering from the photo-sensitive drum.