Provided are an apparatus for feeding sheets, booklets or the like having a wider adjustable range according to the thickness of the object than the conventional apparatus, and a system for sorting forwarding documents with the foregoing feeding apparatus. In the feeding apparatus, a moving shaft is supported by a fixed sleeve so as to be movable upward and downward. A main compression coil spring is located between the moving shaft and the fixed base and imparts a main spring force to the moving shaft in order that an overlap feed limiting member is pressed against a conveying belt. A sub compression coil spring imparts an oppositely directed sub spring force to the moving shaft. A position of a pressing washer is displaced downward by a threading engagement of an upper end adjusting bolt, so that even when the spring force of the main compression coil spring is increased, an increased amount is cancelled by an increase in the spring force of the sub compression coil spring.