The flat lighting assembly apparatus comprises: a ceiling member; a power supply controller disposed within the ceiling member; a connector coupled to the ceiling member and electrically connected to the power supply; and a flat lighting module coupled to the connector and comprising; a frame including a base, an extension portion extending from the base, a socket disposed on a rear surface of the base, and a guide disposed on the rear surface of the base and disposed around the socket; a light source disposed on a front surface of the base; and a diffusion plate disposed on the light source and coupled to the base, wherein the connector has a insertion groove electrically connected to the socket and comprises a coupling unit coupled to the guide.