The intermediate tray of a copying machine for copying on both sides of recording paper or recording paper feeding apparatus incorporates a mechanism for loosening and separating recording papers by air blow in order to prevent duplicate feed. Conventionally, such constitution could not be commonly applied to recording papers of plural sizes, and the recording paper vibrated due to the air flow to give off a loud noise. In the invention, the air flow is formed by plural nozzles arranged in the widthwise direction of the recording paper, and the nozzles near the both ends are controlled by opening and closing depending on the paper size. When the recording paper is conveyed by vacuum attracting to the belt, the recording paper is attracted closely to the belt, eliminating the space for allowing the air flow to enter in, so that vibration may be prevented.