Disclosed are a radio transmission device and a radio transmission method which reduce the RACH conflict ratio and improve the RACH detection characteristic. When the device and the method are used: as the number of signature numbers allocated for UE by the network side increases, the condition for allocating a signature by UE itself is mitigated and an expectation value which is a statistic average value of the RA quantity using the signature allocated by UE for itself is decreased; and as the number of signature numbers allocated for UE by the network side decreases, the condition for allocating a signature by UE itself is limited and an expectation value of the RA quantity using the signature allocated by UE for itself is increased.