To simply and surely detect a mean mobile speed of a mobile base station in a mobile communication system.

A mobile base station 2 receives a transmission signal sent from stationary base stations 1A, 1B, a signal strength measuring section 11 measures the strength of the transmission signal and a data sample section 12 sums the signal strength for each time series. A position estimate section 13 of the mobile base station 2 estimates a position of the mobile base station 2 based on the signal strength. A mobile speed detection section 14 obtains a mean mobile speed of the mobile base station 2 based on time required for the vehicle to move the distance so as to simply detect whether the mobile base station 2 is moving at high speed or low speed.