1. A precoding weight generation method comprising: in a mobile station apparatus, selecting a PMI associated with a precoding matrix including matrix elements corresponding to a stream that most approximates a channel matrix indicative of a channel state in a channel transmission path; transmitting the selected PMI to a base station apparatus as channel information; in the base station apparatus, extracting the matrix elements corresponding to the stream that most approximates the channel state in the channel transmission path from the precoding matrix associated with the PMI transmitted from the mobile station apparatus; and generating precoding weights based on the extracted matrix elements.