1. A data communication system comprising: a wireless terminal including a wireless communication section which carries out wireless transmission/receiving of data; an access point which carries out wireless transmission/receiving of the data with the wireless communication section of the wireless terminal; and a channel determination section which is connected to the access point and which determines a channel to be used when carrying out the wireless transmission/receiving of the data between the wireless terminal and the access point, wherein the channel determination section, carries out calculation processing for quantifying the influence rate of an interfering radio wave and calculating the influence rate as a score for each of a plurality of channels by switching a target channel, for a case where data communication is carried out by use of a radio wave of the channel, on the basis of the influence rate of the interfering radio wave in the target channel among a plurality of usable channels, and determines a channel having the smallest calculated score to be a channel used for wireless transmission/receiving of the data between the wireless terminal and the access point, and classifies the influence rate by the interfering radio wave in the target channel into a first zone where strength of the interfering radio wave is strong enough to cause the access point of the system and an access point of another system to recognize existence of each other, a second zone where the strength of the interfering radio wave is weak enough to be regarded as noise, and a third zone where the strength is intermediate between the first zone and the second zone, sets the score in each of the zones so that the value of the score is higher as transmission/receiving of the data between the wireless terminal and the access point of the system becomes more difficult when the interfering radio wave having the strength of the zone exists, adds the scores of each zone, and calculates the score.