A data communication frame is formed by a preamble portion (PREAMBLE) for demodulation and synchronization, a frame information portion (FC) containing a data type of the frame, a frame length portion (FL), and a data body portion (DATABODY) composed of more than one data packet combined together. If a request to transmit a packet is made from an upper layer, a communication apparatus 10 concurrently performs a process of calculating a frame length the frame would have if combining of the packet is performed and a process of transmitting the preamble portion and the frame information portion. The frame length depends on packets, while the preamble portion and the frame information portion do not depend on packets.