When a frequency channel is shared between adjacent cells in a wireless communication system of time-division duplex operation utilizing a white space, more efficient communications can be achieved. In a wireless communication system of time-division duplex operation utilizing a white space, which is a temporally and spatially unused frequency, to perform wireless communications and having frames in which downstream and upstream subframes are alternately arranged on the time axis, a network controller calculates a common split position, which is to be used in synchronization between base stations sharing a frequency, from collected information in response to a frequency sharing trigger and synchronizes the determined split position between the base stations, thereby allowing the frequency channel to be shared.