A method for feeding sheet materials is disclosed, which is implemented by forwarding a plurality of sheet materials loaded on a loading plate with a rotating feeding roller toward a separation unit, for the leading edge of the sheet materials to be collided with a tapered face of taper member, and subsequently separating the uppermost of the loaded sheet materials through frictional force from the feeding roller after climbing over the taper member to be forwarded further to an image forming unit by way of a nip forming portion, while other underlying sheet materials are halted by the taper member owning to smaller frictional forces there between, thereby obviating the multiple feeding. In addition, the conditions suitable for sheet feeding can be satisfied for various sheet materials different in size and thickness by adjusting the distance between the point of contact of the uppermost sheet material with the feeding roller and that of nip formation, such that modulus values are equated to various sheet materials. As a result, considerably high sheet separation qualities are obtained obviating undue non-feeding or multiple feeding, and various kinds of sheet materials different in size, thickness and coefficient of friction, can be forwarded sheet by sheet securely to image forming unit, thereby achieving satisfactory image formation by means of image forming apparatuses incorporating the sheet feeding apparatuses disclosed herein.