An image forming apparatus includes a charging bias output device, a developing bias output device, a transfer bias output device, and a controller. The controller controls the transfer bias output device to supply a transfer bias from a time at which a first position of a photosensitive member arrives at a transfer position after the charging bias output device starts supplying a charging bias. An initial value of the transfer bias is controlled to be smaller than a normal set value for a predetermined time period (Tc) which is a time after the transfer bias starts to be supplied and within a time corresponding to a rise time (Ta) during which a surface potential of the photosensitive member reaches a predetermined potential after the charging bias starts to be output. The first position of the photosensitive member is a position at which the charging device start charging the photosensitive member.