An image forming apparatus includes a main body portion including an image carrier, an image-carrier driving unit, a latent-image forming unit, a developing-unit attachment section, and a transfer-unit attachment section. The developing-unit attachment section receives a first developing unit having plural developing members or a second developing unit having a single developing member. The transfer-unit attachment section receives a first transfer unit, which includes a first transfer member capable of retaining a recording medium and a first transfer driving unit that rotates the first transfer member, and a second transfer unit, which includes a second transfer member that cannot retain the recording medium. When the first developing unit and the first transfer unit are attached to the developing-unit attachment section and the transfer-unit attachment section, respectively, the first transfer driving unit is mechanically connected to the first developing unit.