In measurement of wireless channels in an IEEE 802.11 wireless local area network (WLAN), in the case of multi-channel measurement as in North America in which eight wireless channels Ch1 through Ch8 are available, channel measurement according to a predetermined algorithm is made in which odd-numbered channels Ch1, Ch3, Ch5 and Ch7 are first measured, and if radio interference occurs in channel Ch5, channels Ch4 and Ch6 adjacent to channel Ch5 are measured. This shortens the measurement time that conventionally corresponds to measurement of the eight channels to the time of six channels, i.e., the sum of the measurement time for the odd-numbered channels and that for the channels adjacent to the interference-occurring channel.