To improve the transmission efficiency of a radio communication system made of a hierarchical structure by surely grasping a down transmission quality irrespective of a radio state.

The communication system evaluates the transmission quality of a radio communication passage between a radio base station 12 and a radio terminal 11 based on transmitting/receiving state of a response 14 for down data and up data, transmits information showing an evaluated result to a radio network controller 13 as feedback information 15, and controls a communication parameter of each layer to be performed between the controller 13 and the terminal 11 based on the information 15.