An image forming apparatus comprising: a first photosensitive member (51K; 51C); a second photosensitive member; a third photosensitive member; a first charger (52K; 52C) that is configured to charge the first photosensitive member (51K; 51C); a second charger that is configured to charge the second photosensitive member; a third charger that is configured to charge the third photosensitive member; a first voltage applying circuit connected to the first charger (52K; 52C) and configured to apply a voltage to the first charger (52K; 52C); and a second voltage applying circuit, which is commonly connected to the second charger and the third charger, and which is configured to apply a voltage to the second charger and the third charger, the first voltage applying circuit is the only voltage applying circuit connected to the first charger (52K; 52C), and is configured to apply a voltage solely to the first charger (52K; 52C), and characterized in that the first charger (52K; 52C), the second charger and the third charger are scorotron type chargers, wherein the first charger (52K; 52C), the second charger and the third charger comprises a wire and a grid, respectively, and wherein the image forming apparatus further comprises: a current detection unit (R2, R3) that is configured to detect grid current values flowing in the grids of the second charger and the third charger; and a controller that is configured to control the second voltage applying circuit based on the grid current values detected by the current detection unit (R2, R3) so as to make the respective grid current values become a predetermined value or greater, wherein the controller is further configured to: determine a grid current indicating the smallest current value of the respective grid current values based on the grid current values detected by the current detection unit (R2, R3); and control the second voltage applying circuit so as to make the grid current indicating the smallest current value become a constant current of the predetermined value or greater. a first photosensitive member (51K; 51C); a second photosensitive member; a third photosensitive member; a first charger (52K; 52C) that is configured to charge the first photosensitive member (51K; 51C); a second charger that is configured to charge the second photosensitive member; a third charger that is configured to charge the third photosensitive member; a first voltage applying circuit connected to the first charger (52K; 52C) and configured to apply a voltage to the first charger (52K; 52C); and a second voltage applying circuit, which is commonly connected to the second charger and the third charger, and which is configured to apply a voltage to the second charger and the third charger, the first voltage applying circuit is the only voltage applying circuit connected to the first charger (52K; 52C), and is configured to apply a voltage solely to the first charger (52K; 52C), and characterized in that the first charger (52K; 52C), the second charger and the third charger are scorotron type chargers, wherein the first charger (52K; 52C), the second charger and the third charger comprises a wire and a grid, respectively, and wherein the image forming apparatus further comprises: a current detection unit (R2, R3) that is configured to detect grid current values flowing in the grids of the second charger and the third charger; and a controller that is configured to control the second voltage applying circuit based on the grid current values detected by the current detection unit (R2, R3) so as to make the respective grid current values become a predetermined value or greater, a current detection unit (R2, R3) that is configured to detect grid current values flowing in the grids of the second charger and the third charger; and a controller that is configured to control the second voltage applying circuit based on the grid current values detected by the current detection unit (R2, R3) so as to make the respective grid current values become a predetermined value or greater, wherein the controller is further configured to: determine a grid current indicating the smallest current value of the respective grid current values based on the grid current values detected by the current detection unit (R2, R3); and control the second voltage applying circuit so as to make the grid current indicating the smallest current value become a constant current of the predetermined value or greater. determine a grid current indicating the smallest current value of the respective grid current values based on the grid current values detected by the current detection unit (R2, R3); and control the second voltage applying circuit so as to make the grid current indicating the smallest current value become a constant current of the predetermined value or greater.