The present invention makes it possible to obtain the transmission diversity effect by applying a CDD while reducing the inter-code interference when performing a code multiplexing. When an Ack/Nack signal is transmitted from a user terminal to a base station in an upstream control channel by using an Ack/Nack resource, the signal is code-multiplexed by using a code sequence containing an orthogonal sequence and a cyclic-shifted sequence and transmitted from a plurality of user terminals to the base station. Upon using an aggregation size indicating the number of control signals of the downstream control channel, if the aggregation size is greater than one, it is determined that no resource located at the right of the axis of the cyclic-shifted amount of the cyclic-shifted sequence in the same orthogonal code of the orthogonal sequence is used, and the Ack/Nack signal to which CDD is applied from a plurality of antennas is transmitted by using a resource ACK #0 allocated to the own device and an unused resource ACK #1, which have the same orthogonal code, but have different cyclic-shifted amounts.