A sheet supply apparatus includes: a tray on which a stack of sheets can be placed, an air blowing section that blows air towards the stack of sheets to float at least a topmost sheet, a sucking and conveying section, above the tray, that sucks said floating sheet(s) and conveys said sheet(s) in a prescribed direction, and a first light source that emits a first stripshaped slit light having a vertically extending component such that the slit light crosses at least a first edge of a first floating sheet and a second edge of a second floating sheet. An image capture section captures an image of the first slit light, a calculating section calculates a vertical clearance between the first and second sheets, and an air amount adjusting section adjusts an amount of air to be blown by the air blowing section based on the calculated vertical clearance.