To easily and flexibly control the output power of a wireless position information transmitter according to a change in a situation or the like.

One wireless position information transmitter 10 among a plurality of wireless position information transmitters 10 that are adjacent to one another compares an electric wave arrival range received from the other wireless position information transmitter 10 with an own electric wave arrival range and determines whether an electric wave non-arrival range and an electric wave collision range exist. If those ranges exist, an output power level of each wireless position information transmitter 10 is determined so as to narrow those ranges as much as possible and the determined output power level is transmitted to the adjacent wireless position information transmitter 10.