A radio transmitting apparatus wherein even if a preamble sequence transmitted via any one of the antennas of the radio transmitting apparatus is detected, the order of the space diversity can be determined with reliability and data signals can be normally decoded. In this apparatus, a deciding unit (101) decides preamble sequences the number of which is equal to the order of the space diversity and further decides transmission block intervals the number of which is equal to or greater than the order of the space diversity. An allocating unit (102) sequentially allocates the preamble sequences, the number of which is equal to the order of the space diversity, to the respective antennas, the number of which is equal to the order of the space diversity, within the respective transmission block intervals. The allocating unit (102) allocates different ones of the preamble sequences to the respective antennas at the respective same transmission timings that are within the respective transmission block intervals.