An image forming apparatus having a photosensitive drum bearing an electrostatic image, and a developing sleeve carrying a developer for developing the electrostatic image, the developing sleeve is in non-contact with the photosensitive drum, and is designed to be flexed so that the surface of the developing sleeve may go away from the surface of the photosensitive drum, and the rotation axis of the photosensitive drum and a straight line linking the centers of the cross-sections of the developing sleeve in a direction perpendicular to the developing sleeve at the both end portions may be in the skew relationship so that the value of the difference between the closest distance at the central portion of a maximum electrostatic image forming width and the closest distance at the both end portions thereof may be smaller than the value of the component of the flexure amount of the developing sleeve in the direction of the closest distance.