A thin-film deposition apparatus includes: a housing; a chamber located within the housing and providing an internal space; a platform disposed within the chamber and configured to support a substrate; a reflector disposed within the housing and disposed outside the chamber; a light source disposed between opposing walls of the reflector and configured to radiate light onto the substrate; a light receiver disposed within the housing, spaced apart from the light source with a portion of the reflector therebetween, and having a hole through which light emitted from the substrate is introduced; an optical cable connected to the light receiver and extending to the outside of the housing; and a sensor disposed outside the housing, connected to the optical cable, and configured to measure a temperature of the substrate by analyzing light transmitted from the optical cable.