1. A transmission header compressing device comprising: a header compressor receiving a moving-picture signal including coded moving-picture data and a transmission header, and compressing the transmission header to transmit the moving-picture signal selectively with the compressed transmission header; and a compression control circuit controlling said header compressor, and determining whether or not the moving-picture data included in the moving-picture signal are subjected to intra-frame coding to inhibit, if the moving-picture data are subjected to intra-frame coding, said header compressor from compressing the header.