a channel structure of a mobile communication system including a radio base station having a transmission antenna able to control a beam direction for each of a plurality of mobile stations in a cell . the mobile stations carry out radio communication using a shared channel together with an associated dedicated channel used in association with the shared channel . the shared channel is shared by the mobile stations and allocated to each of the mobile stations per predetermined unit transmission . a first pilot channel is set and dedicatedly used for channel estimation of the shared channel , and a second pilot channel is set and dedicatedly used for channel estimation of the associated dedicated channel .