A radio base station apparatus comprising: a signal generating section configured to generate a first downlink control signal to be transmitted to a mobile terminal apparatus by a physical downlink control channel and a second downlink control signal to be transmitted to the mobile terminal apparatus by an enhanced physical downlink control channel; a control channel multiplexing section configured to multiplex the first downlink control signal on a radio resource of first n symbols, n = 1, 2 or 3, allocated to the physical downlink control channel in a subframe and to frequency-division-multiplex the second downlink control signal on a radio resource which is allocated to the enhanced physical downlink control channel following the symbol where the first downlink control signal is multiplexed in the subframe; a transmission section configured to transmit the first downlink control signal by the physical downlink control channel and the second downlink control signal by the enhanced physical downlink control channel; and a scheduler configured to control an aggregation level of control channel elements to allocate to the physical downlink control channel for the first downlink control signal and to control an aggregation level of control channel elements to allocate to the enhanced physical downlink control channel for the second downlink control signal; wherein the scheduler is configured to restrict the aggregation levels of resource elements to be set for the first downlink control signal and the second downlink control signal in a subframe by setting different aggregation levels between the first downlink control signal and the second downlink control signal. a signal generating section configured to generate a first downlink control signal to be transmitted to a mobile terminal apparatus by a physical downlink control channel and a second downlink control signal to be transmitted to the mobile terminal apparatus by an enhanced physical downlink control channel; a control channel multiplexing section configured to multiplex the first downlink control signal on a radio resource of first n symbols, n = 1, 2 or 3, allocated to the physical downlink control channel in a subframe and to frequency-division-multiplex the second downlink control signal on a radio resource which is allocated to the enhanced physical downlink control channel following the symbol where the first downlink control signal is multiplexed in the subframe; a transmission section configured to transmit the first downlink control signal by the physical downlink control channel and the second downlink control signal by the enhanced physical downlink control channel; and a scheduler configured to control an aggregation level of control channel elements to allocate to the physical downlink control channel for the first downlink control signal and to control an aggregation level of control channel elements to allocate to the enhanced physical downlink control channel for the second downlink control signal; wherein the scheduler is configured to restrict the aggregation levels of resource elements to be set for the first downlink control signal and the second downlink control signal in a subframe by setting different aggregation levels between the first downlink control signal and the second downlink control signal.