A device for manufacturing a display device includes a deposition source; a deposition thickness calculator for calculating a deposition thickness of a deposition material deposited on a substrate; and a controller for controlling a power of a heater which heats the deposition source by comparing the deposition thickness calculated with a reference thickness. The controller controls the power of the heater either at least one time for each substrate on which the thin film is to be deposited or at regular intervals while the deposition material is deposited. Influence of measurement noise that is included in a quartz crystal sensor for measuring a deposition speed may be minimized, and distribution of deposition thickness of an organic light emitting material may be reduced, thereby increasing the yield of the deposition process and producing quality display devices.