Provided is a radio communication mobile station device capable of preventing a transmission delay when a transmission data amount is increased in a radio communication system where persistent scheduling is performed. In this device, an MCS selection unit (104) selects a first MCS if the transmission data amount accumulated in a buffer of a data control unit (105) is smaller than a threshold value and selects a second MCS having a higher MCS level than the first MCS if the transmission data amount is not smaller than the threshold value. Thus, in a mobile station (100), data encoded and modulated according to the first MCS is transmitted during a normal state when the transmission data amount is small, and data encoded and modulated according to the second MCS having a higher MCS level than the first MCS is transmitted when the transmission data amount is increased to a large amount.