A signal transmission method and apparatus provides a digital transmission path and an analog transmission path between a signal output apparatus and a signal input apparatus. An audio/video signal is transmitted from the signal output apparatus to the signal input apparatus over the digital transmission path. When a user requests an on screen display (OSD) from the signal output apparatus, a controlling unit of the signal output apparatus judges a volume of the data to be displayed via the OSD. If the volume exceeds a preset limit, the OSD is transmitted to the signal input apparatus over the analog transmission path. If the volume does not exceed the preset limit, the OSD is transmitted to the signal input apparatus over the digital transmission path. The controlling unit of the signal output apparatus informs a controlling unit of the signal input apparatus of the intended path of the OSD, so that the signal input apparatus can process the OSD in the appropriate manner.