A developing unit for developing an electrostatic latent image formed on the outer peripheral surface of a latent image bearing member rotating in one direction with a developer by mixing electrostatically chargeable toner and magnetic carrier, includes: a developing roller; a carrier collecting roller; a cooling portion including a forced draft duct for airflow from a fan and disposed on the bottom side of the developing vessel; a suctioning portion including a suctioning duct for airflow from suctioning ports disposed on the lower side of the carrier collecting roller, disposed under the forced draft duct; a filter for removing the scattering toner from air including the scattering toner suctioned from the suctioning ports; and, an exhaust portion including an airflow exhaust duct for discharging the air passed through the filter and the forced draft duct to an exhaust port.