Provided is a radio communication base station device capable of acquiring both a multi-user diversity effect and a frequency diversity effect simultaneously in multi-carrier communications. In this device, modulation units (101-1 to 101-n) modulate data to mobile stations (MS#1 to MS#n) individually to create data symbols. A separation unit (102) separates each data symbol inputted, into an Ich (in-phase components) and a Qch (orthogonal components). An Ich arrangement unit (103) and a Qch arrangement unit (104) arrange the Ich and Qch, respectively, in a plurality of sub-carriers constituting an OFDM symbols, and output the same to a synthesization unit (105). This synthesization unit (105) synthesizes the Ich and Qch arranged for each sub-carrier, to create the synthesized symbol.