A radio communication base station device can efficiently obtain a multiuser diversity gain from frequency scheduling while reducing the amount of a reference signal occupying an uplink. In the device, a grouping section divides a plurality of RBs (Resource Blocks) into a plurality of RB groups. An RB group control unit performs a control to change the correspondence relationship between the RBs and the RB groups with time. When the grouping section divides the RBs into the RB groups, the RB control unit performs a control to change a combination of the RBs included in each of the RB groups with time. A scheduling section performs a scheduling of allocating each of a plurality of mobile stations to each of the RBs in each of the RB groups according to the reception quality of the reference signal.