Provided are a radio transmission device and a radio transmission method, which prevent the deterioration of a preamble detecting performance while reducing the collision probability of a RACH. In this radio transmission device, a Signature table storage unit (103) divides the magnitudes of transmission loss levels into individual levels corresponding to the distances from a base station, to cause CAZAC series and circulation shift quantities to correspond to each other at the individual levels, and is provided with a table containing a plurality of Signatures created from the CAZAC series and the circulation shift quantities caused to correspond to each other. A Signature selecting unit (104) selects one of the corresponding Signatures at random from the Signature table storage unit (103), on the basis of the magnitude of the transmission loss level outputted from a transmission loss level deciding unit (102). A RACH signal generating unit (105) generates the RACH signal with the Signature selected.