A communication system includes: an RF/IF/BB unit (21) for receiving, in a mobile station device (20), a transmission signal from a base station device; a received power calculation unit (221) for obtaining received power thereof; a communication rate modification unit (23) for changing a communication rate by changing a modulation scheme used by the base station device to modulate the transmission signal in a predetermined case; and a communication rate increase limit unit (27) for limiting the communication rate to be increased by the communication rate modification unit (23), according to received power required for the mobile station device (20) to demodulate the transmission signal and according to the received power obtained when receiving the transmission signal after the communication rate is changed by the communication rate modification unit (23) and predicted based on the received power obtained by the received power calculation unit (221) and based on a decrease amount of a transmission power of a transmission signal decreased by the base station device according to increase of the communication rate by the communication rate modification unit (23).