A coding apparatus generates coded data by coding inputted data in a predetermined unit basis, maps one or more units of the coded data onto a packet of fixed length and outputs the packet. The coding apparatus includes a storage unit that stores the coded data and outputs the data size of the stored coded data, and a packetization unit that maps the coded data stored in the storage unit onto the packet and outputs the header size assigned to the one or more units of the coded data and the payload size of the packet. The coding apparatus also includes a control unit that generates the control information based on the data size of the outputted coded data, the header size and the payload size and outputs the control information, and a coding unit that generates the coded data by calculating an outer candidate value that makes the data size of the coded data to be mapped onto the packet an integral multiple of the payload size of the packet based on the outputted control information and coding the predetermined units of inputted data up to the outer candidate value.