A radio terminal apparatus adapted to perform communication using an uplink component band and a plurality of downlink component bands associated with the uplink component band, the radio terminal apparatus comprising: a radio reception section for receiving a control signal including allocation information, per downlink component band; and a control signal reception processing section for determining a basic information size used in: reception processing on the control signal in each downlink component band and for performing the reception processing on the control signal based on the basic information size, characterized in that: in a basic downlink component band including uplink resource allocation information and downlink resource allocation information, the basic downlink component band being part of the plurality of downlink component bands, the control signal reception processing section is adapted to determine the basic information size based on a bandwidth of the basic downlink component band, when an information size determined based on the bandwidth of the basic downlink component band is greater than an information size determined based on a bandwidth of the uplink component band; the control signal reception processing section is adapted to determine the basic information size based on a bandwidth of the uplink component band, when the information size determined based on the bandwidth of the basic downlink component band is smaller than the information size determined based on the bandwidth of the uplink component band; and with respect to other downlink component bands, being a remaining part of the plurality of downlink component bands, including only downlink resource allocation information, the control signal reception processing section is adapted to determine the basic information size based on the bandwidth of respective one of the other downlink component bands regardless of the bandwidth of the uplink component band. a radio reception section for receiving a control signal including allocation information, per downlink component band; and a control signal reception processing section for determining a basic information size used in: reception processing on the control signal in each downlink component band and for performing the reception processing on the control signal based on the basic information size, characterized in that: in a basic downlink component band including uplink resource allocation information and downlink resource allocation information, the basic downlink component band being part of the plurality of downlink component bands, the control signal reception processing section is adapted to determine the basic information size based on a bandwidth of the basic downlink component band, when an information size determined based on the bandwidth of the basic downlink component band is greater than an information size determined based on a bandwidth of the uplink component band; the control signal reception processing section is adapted to determine the basic information size based on a bandwidth of the uplink component band, when the information size determined based on the bandwidth of the basic downlink component band is smaller than the information size determined based on the bandwidth of the uplink component band; and with respect to other downlink component bands, being a remaining part of the plurality of downlink component bands, including only downlink resource allocation information, the control signal reception processing section is adapted to determine the basic information size based on the bandwidth of respective one of the other downlink component bands regardless of the bandwidth of the uplink component band. in a basic downlink component band including uplink resource allocation information and downlink resource allocation information, the basic downlink component band being part of the plurality of downlink component bands, the control signal reception processing section is adapted to determine the basic information size based on a bandwidth of the basic downlink component band, when an information size determined based on the bandwidth of the basic downlink component band is greater than an information size determined based on a bandwidth of the uplink component band; the control signal reception processing section is adapted to determine the basic information size based on a bandwidth of the uplink component band, when the information size determined based on the bandwidth of the basic downlink component band is smaller than the information size determined based on the bandwidth of the uplink component band; and with respect to other downlink component bands, being a remaining part of the plurality of downlink component bands, including only downlink resource allocation information, the control signal reception processing section is adapted to determine the basic information size based on the bandwidth of respective one of the other downlink component bands regardless of the bandwidth of the uplink component band.