A storage unit stores a preamble signal defined in a legacy system and a preamble signal defined in a MIMO system. A monitoring unit in a transmitting apparatus monitors the existence of any communication apparatus which is not compatible with the MIMO system but accepts the legacy system. A channel characteristics acquiring unit derives the characteristics of a radio channel between the transmitting apparatus and a receiving apparatus. A selector selects a packet format based on a monitoring result obtained by the monitoring unit. The selector also selects where to place LTS, based on the characteristics of wireless channel derived by the channel characteristics acquiring unit.