In a mobile radio network in which synchronous base stations and asynchronous base stations coexist, according to handover destination base station candidate information transmitted from a base station to a mobile station, effective time information indicating either an effective time during which it is guaranteed that a signal from a base station candidate included in the handover destination base station candidate information can be detected when, after a lapse of an integral multiple of a fixed time interval from a time when the mobile station could detect a reference signal which were transmitted at the fixed time intervals from the base station candidate, the mobile station detects the same base station candidate again, the effective time depending on the base station candidate, or an index for enabling the mobile station to drive the effective time is provided to the mobile station, and the mobile station carries out the detection by setting up the detection time intervals at which the mobile station detects a signal from the base station candidate on the basis of the effective time information.