A base station measures a signal to interference power ratio using a control signal received from a terminal device through wireless communication, and decides an MCS value indicating a combination of a modulation scheme and a channel code rate. The base station includes the decided MCS value in uplink-channel transmission information and transmits the MCS value to the terminal device by using a control channel including downlink scheduling information. The terminal device decides a transmission format of an uplink data channel based on the MCS in the uplink-channel transmission information. The terminal device, when having received a downlink data channel from the base station, decides a response content (ACK/NACK/DTX) to the base station, based on the result of decoding the downlink data channel. Thereafter, the terminal device transmits the decided response content to the base station through the uplink data channel using the decided transmission format.