an image forming apparatus includes a rotatable drum , a charging section for charging the drum , a latent image forming section , a potential detector , a phase detector , and a controller . the charging section includes a first carrying member and a second carrying member for carrying electroconductive magnetic particles . the second carrying member is disposed downstream of said first carrying member . the latent image forming section forms a latent image on the drum , and is disposed downstream of the charging section . the potential detector detects a surface potential of the drum , and is disposed downstream of the charging section . the phase detector detects information relating to a rotational phase of the second carrying member . the controller controls voltages applied to the first carrying member and to the second carrying member , on the basis of a result of detection by the potential detector and a result of detection by the phase detector .