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 .