A negatively-chargeable non-magnetic one-component developer for developing an electrostatic latent image using a contact DC-bias development method, having a capacitance of 1.05×10−12 to 1.25×10−12 F, a volume resistivity of 5.0×1010 to 5.0×1012 Ω·cm and a dielectric loss tangent of 1.0×10−3 to 2.0×10−2. In a contact DC-bias development method, the developer has a capacitance of 1.30×10−12 to 1.60×10−12 F, a resistivity of 5.0×109 to 5.0×1010 Ω·cm and a dielectric loss tangent of 1.0×10−3 to 2.0×10−2. In a non-contact DC/AC-bias development method, the developer has a capacitance of 1.45×10−12 to 1.60×10−12 F, a resistivity of 5.0×109 to 1.0×1010 Ω·cm and a dielectric loss tangent of 1.0×10−3 to 2.0×10−2.