<p>A wireless base station (eNB) is provided with an aggregation level decision unit (14) that determines an aggregation level based on a CQI notified from a mobile station (UE), a control channel element assignment unit that assigns multiple consecutive CCEs to the PDCCH addressed to the mobile station (UE) based on the determined aggregation level, and a resource assignment unit (14) that assigns a resource element group constituting the assigned CCEs as the resources for the PDCCH addressed to the mobile station (UE). A control channel element assignment unit (14) assigns multiple consecutive CCEs to the PDCCH addressed to the mobile station (UE) based on an aggregation level that has been changed by the aggregation level decision unit (14) when the assignment of the CCEs to the PDCCH addressed to the mobile station (UE) fails.</p>
