An image forming apparatus comprising: a rotatable image bearing member; a charging member configured to form a charging portion by contacting the image bearing member and charge a surface of the image bearing member at the charging portion; a transfer member configured to form a transfer portion by contacting the image bearing member and transfer a region of the image bearing member where a surface potential is formed on the surface of the image bearing member charged by the charging member at the transfer portion; charging voltage application means for applying a charging voltage including only a direct-current component to the charging member; transfer voltage application means for applying a transfer voltage to the transfer member; detection means for detecting a transfer current flowing from the transfer member to the image bearing member; and control means configured to control the charging voltage application means and the transfer voltage application means, characterized in that the control means is configured to, with the image bearing member rotating, control the charging voltage application means to apply the charging voltage to the charging member so as to form the surface potential on the region and to control the transfer voltage application means so as to apply the transfer voltage the same in polarity as the charging voltage to the transfer member, and wherein, when an absolute value of the surface potential formed on the region of the image bearing member immediately before entry into the charging portion is larger than an absolute value of the surface potential formed on the region of the image bearing member when it is positioned upstream of the transfer portion and downstream of the charging portion in a rotational direction of the image bearing member, the detection means detects the transfer current when the region passes through the transfer portion with the transfer voltage applied to the transfer member during one rotation of the image bearing member after the region passes through the charging portion. a rotatable image bearing member; a charging member configured to form a charging portion by contacting the image bearing member and charge a surface of the image bearing member at the charging portion; a transfer member configured to form a transfer portion by contacting the image bearing member and transfer a region of the image bearing member where a surface potential is formed on the surface of the image bearing member charged by the charging member at the transfer portion; charging voltage application means for applying a charging voltage including only a direct-current component to the charging member; transfer voltage application means for applying a transfer voltage to the transfer member; detection means for detecting a transfer current flowing from the transfer member to the image bearing member; and control means configured to control the charging voltage application means and the transfer voltage application means, characterized in that the control means is configured to, with the image bearing member rotating, control the charging voltage application means to apply the charging voltage to the charging member so as to form the surface potential on the region and to control the transfer voltage application means so as to apply the transfer voltage the same in polarity as the charging voltage to the transfer member, and wherein, when an absolute value of the surface potential formed on the region of the image bearing member immediately before entry into the charging portion is larger than an absolute value of the surface potential formed on the region of the image bearing member when it is positioned upstream of the transfer portion and downstream of the charging portion in a rotational direction of the image bearing member, the detection means detects the transfer current when the region passes through the transfer portion with the transfer voltage applied to the transfer member during one rotation of the image bearing member after the region passes through the charging portion.