A cognitive terminal includes different types of radio modules suiting to different types radio media employed by a cognitive base station in the radio communication system. The radio module of the cognitive terminal counts the number of times it receives/transmits ACK/NACK in each unit time. A radio environment cognition unit of the cognitive terminal performs calculations using the count number(s) in consideration of the packet transmission time interval or the time required for repeating a single data packet, thus measuring characteristics of delay time variations in uplink/downlink communication with respect to each radio media. Thus, it is possible for the cognitive terminal to switch over radio media based on ACK/NACK in uplink/downlink communication.