To prevent communication faults which are caused by the insufficient capability of a master unit about an ad hoc network system that consists of plural slave units and a master unit.

An ad hoc network is reconstructed with the optimum radio terminal as a master unit made its master unit, by deciding an interim master unit 101 among plural radio terminals which can be either a master unit or a slave unit, collecting a transfer rate that is measured by using a test signal and the remaining amount of battery of each slave unit 102 to 104 by the unit 101, when data exchange is available between the other radio terminals 102 to 104 and the unit 101 and newly reselecting a true master unit based on collected information.