This invention achieves lower electric power consumption of a sensor node for carrying out an intermittent operation, in a sensor net system. A time when the sensor node transmits a signal to a base station is estimated. Then, in accordance with the estimation, a table for storing a signal transmitted from the sensor node is installed in a wireless section of the base station. Consequently, a communication time between the sensor node and the base station can be made shorter. Also, a start time of a micro computer is set for RTC inside the sensor node, so the micro computer inside the sensor node can be put in the standby state.