To provide a radio base station apparatus and mobile terminal supporting each of a plurality of mobile communication systems when the plurality of mobile communication systems coexists, the radio base station apparatus assigns a modulated signal of a control signal to at least one frequency band with the system band of the LTE system as a unit on a predetermined data block basis (CCE basis) according to a predetermined rule, and when data blocks are assigned according to the rule as shown in FIG. 4(a), the mobile terminal demodulates CCEs of the same number in respective frequency bands at a time and thereby determines whether or not the signal is the control signal to the mobile terminal. Meanwhile, when data blocks are assigned according to the rules as shown in FIGS. 4(b) and 4(c), the mobile terminal demodulates a specific CCE block range in each frequency band, and thereby determines whether or not the signal is the control signal to the mobile terminal.