Measurement request and response for reception quality based notified cell identification

A mobile communication system including a base station which sets a plurality of cells and a mobile station is provided. In the mobile communication system, the base station notifies the mobile station in communication through a first cell among the plurality of cells, of the identification information of at least one cell among the plurality of cells, which can be used for communication with the mobile station and instructs the mobile station to measure a reception state of radio signals. The mobile station detects, in response to the instruction from the base station, a cell for transmitting radio signals which the mobile station is able to receive, and when identification information of the detected cell matches any of the identification information of the at least one cell, the mobile station notifies the base station of the identification information of the detected cell.