A radio base station including a resource assignment unit configured to determine a time direction resource, a frequency direction resource, and a code direction resource which are to be assigned as a reception quality notification resource that should be used for notifying each mobile station of a reception quality in a downlink, the resource assignment unit is configured to determine the time direction resources and the frequency direction resources, which are to be assigned as the reception quality notification resource, and then determine the code direction resources to be assigned as the reception quality notification resource the resource assignment unit is configured to assign, as the reception quality notification resource, in order from a frequency direction resource with a lower usage rate of the code direction resource, within each time direction resource.