An information data transmission system deals with a plurality of kinds of information data different in quantity from one another and respectively corresponding to prescribed amounts of an information signal. The system has first encoding circuitry for encoding the plurality of kinds of information data and second encoding circuitry for predictively encoding the plurality of kinds of information data. The timing of the production of outputs from the first and second encoding circuits is such that, for all kinds of the plurality of information data, the quantity of information data encoded by the first encoding circuitry is equalized.