A communication terminal which modulates and demodulates a packet for transmission and reception based on a communication parameter for modulation and demodulation determined according to a communication-medium characteristic. The communication terminal includes: an extracting unit which extracts, during every occurrence of a predetermined cycle, information indicative of either one of transmission efficiency and reception quality of the packet as an information element; a calculating unit which calculates a difference between a first information element extracted by the extracting unit and a second information element previously extracted by the extracting unit; and detecting-scheme performance determining unit which determines, based on the difference between the first information element and the second information element whether a scheme of detecting the communication-medium characteristic is to be performed.