A signal transmission apparatus includes: a multiplex unit generating B/Rch by multiplexing image signals read from B, R pixels arranged in the same sample alternately on active regions corresponding to Cch in HD-SDI with a start code similar to SAV or EAV, in which image signals sequentially read in a line direction and inputted with a given number of samples from an imaging device having an RGB full pixel structure in which R, G and B pixels disposed in one sample respectively output R, G and B image signals, as well as generating Gch by sequentially multiplexing image signals read from samples of G pixels adjacent in the line direction on active regions corresponding to Ych in HD-SDI with the start code; and an 8B/10B encoder outputting serial digital data obtained by 8B/10B encoding and converting active regions in the B/R ch and the Gch having the data structure corresponding to HD-SDI as well as auxiliary data regions including SAV, EAV, LN and CRCC.