The disclosed radio base station (eNB) is provided with a Physical Uplink Shared Channel (PUSCH) resource allocator (11A) which allocates PUSCH resources to a PUSCH of a mobile station (UE); a Physical Hybrid-ARQ Indicator Channel (PHICH) resource allocator (11B) which allocates a first frequency direction resource and a first code direction resource to a PHICH based on identifying information of a PUSCH resource; and a notifier (12) which notifies the mobile station (UE) of the PUSCH resource. The PHICH resource allocator (11B) changes the frequency direction resource and code direction resource allocated to a PHICH from the first frequency direction resource and the first code direction resource to a second frequency direction resource and a second code direction resource when the usage conditions of the code direction resource of the first frequency direction resource meet predetermined conditions.
