A method and apparatus for outputting a supplementary content from a WFD is disclosed. The method for outputting a supplementary content from a WFD may comprise the steps of: after a WFD source is connected to a WFD, transmitting, by the WFD source, an RTSP parameter request message on the basis of an RTSP to a WFD sink in order to perform a capability negotiation procedure with the WFD sink; transmitting, by the WFD source, an RTSP parameter response message to the WFD sink in response to the RTSP parameter request message; and after performing the capability negotiation procedure, transmitting, by the WFD source, a transmission stream, obtained by overlapping and multiplexing a video stream including video data having a first resolution and a supplementary stream including supplementary data having a second resolution, to the WFD sink, wherein a WFD discovery response frame includes second resolution-related information for determining the second resolution, and an RTSP parameter response frame includes the second resolution-related information.