An image forming apparatus includes an image bearing member, a developing device, first and second drive portions, and a controller. The developing device includes first, second, and third conveying screws, and a developer bearing member. A ratio of a rotational driving speed (Vsc) of the first and second conveying screws by the first drive portion to a rotational driving speed (Vs1) of the developer bearing member by the second drive portion is Vsc/Vs1. A ratio of a rotational driving speed (Vsc3) of the third conveying screw by the second drive portion to the developer bearing member rotational driving speed (Vs1) is Vsc3/Vs1. In a control mode, the controller controls the first and second drive portions so that Vsc/Vs1 in a non-image forming period becomes less than Vsc/Vs1 in an image forming period such that Vsc3/Vs1 in the non-image forming period is equal to Vsc3/Vs1 in the image forming period.