PURPOSE: To communicate with a base station without competition between mobile stations, by asynchronously sampling and detecting a signal from the base station at the plural mobile stations.

CONSTITUTION: A base station transmits a signal having a fixed length tt at a constant interval tr. Each mobile station samples a received signal on the basis of a clock signal outputted from the self-station. The sampling interval is shorter than tt or tr. Detecting the signal from the base station, each mobile station transmits data stored in the self-station to the base station while the mobile station stops its transmission. A mobile station must immediately stop transmission from the self-station when the timing to detect the stop of transmission from the base station is different in each mobile station, the time required from detection to transmission is short, and another mobile station starts transmission; so that confliction between the mobile stations is prevented.