A radio base station apparatus used in a radio communication system in which an initiator holds a transmission opportunity (TXOP) period in a frame exchange sequence and a responder responds to the initiator in the frame exchange sequence is disclosed. The apparatus includes a setting device which sets a ratio between a first period necessary for transmitting a first frame from the initiator to the responder and a second period necessary for transmitting a second frame from the responder to the initiator. The apparatus also includes a calculation device which calculates the first period to be used by the initiator and the second period to be used by the responder, on the basis of the transmission opportunity period and of the ratio which is set.