An electric field intensity measuring circuit measures the electric field intensity of each of multiple communication channels available for data communication. A channel determiner compares electric field intensities measured by an electric field intensity measuring circuit with multiple different thresholds including a first threshold as the carrier sense threshold and a second threshold that is the detrimental interference level the interference of which causes the reception sensitivity to deteriorate, counts the numbers of times that the electric field intensity exceeds the thresholds on each communication channel, and selects a communication channel for use based on the counted numbers of times that the thresholds have been exceeded on the communication channels.