An object of the present invention is to prevent an electrical breakdown of a toner layer and an occurrence of overcurrent, thereby preventing quality of image from being degraded at the time of development, when development with one-component toner is conducted using a developing roller of low resistance. The resistance value Rd of a developing roller (41) which carries and conveys one-component toner (10) in a manner of coming into contact with a photoconductor (1) which bears an electrostatic latent image, is defined as Rd = ρd · (Dd1/S1), wherein S1 (cm 2 ) is an area in which the developing roller (41) comes into contact with the static image bearing member via a toner layer (45), Dd1 (cm) is a layer thickness of a semiconductive layer which composes the developing roller, and ρd (Ω · cm) is a volume resistivity thereof. The range of the resistance Rd is set as 10 4 5 and the resistance Rt (Ω) of the toner layer is set as Rt > 5 × 10 7 . By using the developing roller (41) of low resistance, excellent development is realized and an electrical breakdown and an overcurrent can be avoided by the resistance value of the toner layer.