The present invention is designed to make it possible to apply power scaling to a period where the upper limit value is exceeded, while maintaining uplink transmission quality. In a radio communication system 1 in which multiple cells (C1 and C2) are formed, a base station apparatus (20) forms a first cell C1, which is one of the multiple cells, and has a control section (234) that controls uplink transmission times per timing group, which includes one component carrier or a plurality of component carriers, and a transmission section (106) that signals a timing group or a component carrier determined as a target of power scaling, as power scaling target information, in which the timing group or the component carrier, to which power scaling is applied, is expressly determined, to a the user terminal (10).