Provided are a radio terminal device, a radio base station device, and a channel signal forming method which can prevent quality degradation of the downlink source allocation information by reducing the frequency of the zero information addition process to the downlink resource allocation information when executing communication using an uplink unit band and a plurality of downlink unit bands correlated to the uplink unit band. A base station can execute communication using the uplink unit band and a plurality of downlink unit bands correlated to the uplink unit band. The base station includes: a PDCCH generation unit which includes the uplink allocation information relating to the uplink unit band only in some of the channel signals formed for each of the downlink unit bands; and a padding unit which adds zero information to the downlink allocation information only in the selected some channel signals having the bandwidth of the corresponding downlink unit band smaller than that of the uplink unit band until the downlink allocation information size becomes equal to the uplink allocation information size.