An image forming apparatus arranged to form a developer image by making a developer adhere onto an electrostatic latent image formed on an image holding body and to transfer the developer image onto an image forming medium by using a transferring member to form an image, and to comprise a power source for applying a voltage to the transferring member, wherein: the power source for generating a transfer voltage of 5000 or less, is used for transferring the developer image onto the image forming medium by supplying the transfer voltage in a range 500 to 2000 to the transferring member; the transferring member has a first resistance value when supplied with a voltage of 500 V, a second resistance value when supplied with a voltage of 1000 V and a third resistance value when supplied with a voltage of 2000 V, the first, second, and third resistance values being measured under a prescribed normal temperature value of 20°C and a prescribed normal humidity value of 50%; the transferring member contains a material with electron conductivity and a material with ion conductivity, the material with electron conductivity including at least one of carbon black, carbon quality fiber, copper particle, silver particle and nickel, and the material with ion conductivity being alkali metal salt, wherein a weight part of the material with electron conductivity and a weight part of the material with ion conductivity are such that a ratio of the second and the first resistance value measured under prescribed normal temperature value and prescribed normal humidity value is between 0.5 and 0.89, and a ratio of the third and the second resistance value measured under prescribed normal temperature value and prescribed normal humidity value is between 0.3 and 0.88; the transferring member can be used in environmental conditions of the temperature value of 10°C and the humidity value of 20%, and can be used in environmental conditions of a temperature value of 28 °C and a humidity value of 80%; the rotating transferring member generates a variation of the transfer voltage in the circumferential direction, the variation of the transfer voltage of 6 is allowable in the case of generating the transfer voltage of 2000; the power source is configured to change a transfer current by 1 μA in response to a change in voltage larger than 6 V when a voltage of 2000 V is applied with reference to a control table for changing the transfer voltage by a change amount larger than 6 and changing the transfer current at a pitch of 1 [μA]; and wherein, in the case where the image being formed under environmental conditions of the temperature value of 10°C and the humidity value of 20 %, the power source can supply a transfer current of 10 μA or more to the transferring member in response to a voltage of 5000 V or less, and the resistance of the transferring member upon manufacturing is set to 2.77 × 10 8 [Ω] or less. the power source for generating a transfer voltage of 5000 or less, is used for transferring the developer image onto the image forming medium by supplying the transfer voltage in a range 500 to 2000 to the transferring member; the transferring member has a first resistance value when supplied with a voltage of 500 V, a second resistance value when supplied with a voltage of 1000 V and a third resistance value when supplied with a voltage of 2000 V, the first, second, and third resistance values being measured under a prescribed normal temperature value of 20°C and a prescribed normal humidity value of 50%; the transferring member contains a material with electron conductivity and a material with ion conductivity, the material with electron conductivity including at least one of carbon black, carbon quality fiber, copper particle, silver particle and nickel, and the material with ion conductivity being alkali metal salt, wherein a weight part of the material with electron conductivity and a weight part of the material with ion conductivity are such that a ratio of the second and the first resistance value measured under prescribed normal temperature value and prescribed normal humidity value is between 0.5 and 0.89, and a ratio of the third and the second resistance value measured under prescribed normal temperature value and prescribed normal humidity value is between 0.3 and 0.88; the transferring member can be used in environmental conditions of the temperature value of 10°C and the humidity value of 20%, and can be used in environmental conditions of a temperature value of 28 °C and a humidity value of 80%; the rotating transferring member generates a variation of the transfer voltage in the circumferential direction, the variation of the transfer voltage of 6 is allowable in the case of generating the transfer voltage of 2000; the power source is configured to change a transfer current by 1 μA in response to a change in voltage larger than 6 V when a voltage of 2000 V is applied with reference to a control table for changing the transfer voltage by a change amount larger than 6 and changing the transfer current at a pitch of 1 [μA]; and wherein, in the case where the image being formed under environmental conditions of the temperature value of 10°C and the humidity value of 20 %, the power source can supply a transfer current of 10 μA or more to the transferring member in response to a voltage of 5000 V or less, and the resistance of the transferring member upon manufacturing is set to 2.77 × 10 8 [Ω] or less.