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.