To provide a radio data transmission system which efficiently transmits data by efficiently selecting UPCH function channel for conducting a packet communication.

The radio data transmission system comprises: a mobile unit 10; a radio base station 20 for recording number-of-moving-units information having UPCH function channel using the mobile unit 10 and identification information of the mobile unit; and a number-of-moving stations managing unit 30 for transmitting the number-of-mobile units information using the UPCH function channel of each UPCH function channel as control information to the radio base station 20 for controlling the channel to be controlled, by acquiring the number-of-mobile units information from the station 20 and detecting more UPCH function channel than a predetermined threshold from the number of the mobile units to be used. The base station 20 transmits the control information to the mobile unit 10 using the channel to be controlled. The mobile unit 10 using the channel to be controlled selects the UPCH function channel of smaller number of the using mobile units from the control information and communicates the data.