To simply detect the position of an article in a space by sticking an IC tag on the article with a multitude of IC tag readers disposed in the space while preventing an article having no gate from being stolen or moved without notice, with respect to an IC tag position determining device and an IC tag position determining method for determining the position of an article with an IC tag stuck thereon.

This IC tag position determining device is equipped with an IC tag reader for reading information from an IC tag by radio, a means for measuring the intensity of a signal when information becomes readable from the tag reader or when it becomes unreadable therefrom while changing the intensity of the signal used for reading the information possessed by the IC tag; a means for calculating the distance to the IC tag based on the measured intensity; and a means for calculating the position of the article based on, at least two, that is, the calculated distance and the position of the tag reader.