A radio communication system comprising a group of mobile station apparatuses to have varying numbers of receive antennas, and a base station apparatus to transmit data to the group of mobile station apparatuses via a plurality of transmit antennas, wherein: each mobile station apparatus in the group of mobile station apparatuses comprises: a number of receive antennas notifying signal transmit section that transmits a number of receive antennas notifying signal indicating the number of receive antennas provided for the mobile station apparatus; and the base station apparatus comprises: a number of receive antennas notifying signal receive section that receives the number of receive antennas notifying signals; a transmit order determining section that determines order in which data are transmitted based on the number of receive antennas notifying signals received; and a data transmit section that assigns the data to the plurality of transmit antennas according to the determined transmit order and transmits the data; and characterised in that the transmit order determining section determines the transmit order so as to transmit the same number of different data as the receive antennas of a mobile station apparatus having a smallest number of receive antennas, among mobile station apparatuses as partners to which data is transmitted simultaneously via the plurality of transmit antennas. a number of receive antennas notifying signal transmit section that transmits a number of receive antennas notifying signal indicating the number of receive antennas provided for the mobile station apparatus; and the base station apparatus comprises: a number of receive antennas notifying signal receive section that receives the number of receive antennas notifying signals; a transmit order determining section that determines order in which data are transmitted based on the number of receive antennas notifying signals received; and a data transmit section that assigns the data to the plurality of transmit antennas according to the determined transmit order and transmits the data; and characterised in that the transmit order determining section determines the transmit order so as to transmit the same number of different data as the receive antennas of a mobile station apparatus having a smallest number of receive antennas, among mobile station apparatuses as partners to which data is transmitted simultaneously via the plurality of transmit antennas. a number of receive antennas notifying signal receive section that receives the number of receive antennas notifying signals; a transmit order determining section that determines order in which data are transmitted based on the number of receive antennas notifying signals received; and a data transmit section that assigns the data to the plurality of transmit antennas according to the determined transmit order and transmits the data; and characterised in that the transmit order determining section determines the transmit order so as to transmit the same number of different data as the receive antennas of a mobile station apparatus having a smallest number of receive antennas, among mobile station apparatuses as partners to which data is transmitted simultaneously via the plurality of transmit antennas.