PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of appropriately controlling a voltage value or a current value applied to a charging member for electrically charging toner even when there is a fluctuation of electric resistance of the charging member which electrically charges toner on a belt body, or of the charging member and the belt body.SOLUTION: An image forming apparatus 100 comprises: an image carrier 1; a belt body 10; a contact member 14; a first power supply 15 which applies a current or a voltage to the contact member 14; first detection means 18 which detects the current or the voltage which the first power supply 15 outputs; a charging member 17 which electrically charges toner on the belt body 10; a second power supply 70 which applies a current or a voltage to the charging member 17; second detection means 71 which detects the current or the voltage which the second power supply 70 outputs; and determination means 111 which determines the voltage value or the current value to apply to the charging member 17 in such a manner that the electric potential of the charging member 17 is at a target value or a value in a target range by using a detection result of the first detection means 18 and a detection result of the second detection means 71.