An image forming apparatus is configured to reduce follow-up delay in impedance fluctuation and to reduce an accuracy fall in power supply control. The image forming apparatus includes a transfer element, a supply element, a detection element, a modification element, and a switch element. The supply element supplies electricity that depends on a set value to the transfer element. The detection element detects the control object value supplied to the transfer element. Depending on a difference between the control object value detected by the detection element and a target value, the modification element operates modification of the set value. The switch element switches between a short interval mode and a long interval mode. In a short interval mode, an execution time interval for modification of the set value is shorter, while, in a long interval mode, the execution time interval for modification of the set value is longer.