A mobile station apparatus is provided that performs receive processing efficiently and reduces unnecessary power consumption. In this mobile station apparatus, a signaling detector (71) detects a compressed mode gap period in an uplink channel, that is, a period in which no uplink signal is transmitted to a base station, and reports this period to a controller (72). If the period detected in the signaling detector (71) contains transmission timing of an ACK/NACK signal, the controller (72) controls an HS-PDSCH receive processor (40) to stop the receive processing of the packet data corresponding to the ACK/NACK signal.