A thin film deposition apparatus that can be easily used to manufacture large-sized display devices on a mass scale and that improves manufacturing yield, and a method of manufacturing an organic light-emitting display device by using the thin film deposition apparatus. The thin film deposition apparatus includes: a loading unit to place a substrate, which is a deposition target, on an electrostatic chuck; a deposition unit including a chamber, and a thin film deposition assembly that is disposed in the chamber and forms a thin film on the substrate placed on the electrostatic chuck; an unloading unit to separate the substrate on which deposition is completed from the electrostatic chuck; a first conveyor unit to sequentially move the electrostatic chuck having the substrate thereon to the loading unit, to the deposition unit, and finally, to the unloading unit, wherein the first conveyor unit includes: one pair of first guide rails and one pair of second guide rails disposed in parallel; at least one first guide block engaged with the first guide rails, respectively; and at least one second guide block engaged with the second guide rails, respectively.