PROBLEM TO BE SOLVED: To provide a device power saving method for a radio system which is composed of a master unit and a plurality of slave units.SOLUTION: The master unit transmits a synchronization request signal to each slave unit at each first time interval. The slave unit receives the synchronization request signal at the interval of an integral multiple of the first time interval, to periodically establish synchronization with the master unit. The slave unit, after being synchronized, transmits control data or collection data to the master unit at each second time interval based on the first interval. After the transmission, the slave unit is operated in a low power consumption mode before transmitting the next data after the second time interval. The master unit, after the data reception, is operated in the low power consumption mode before the transmission of the next synchronization request signal after the first time interval. The slave unit transmits data only, other than receiving the synchronization request signal from the master unit. The slave unit shifts to the low power consumption mode immediately the after transmission to save the power. The master unit is activated from the low power consumption mode according to the data reception from the slave unit, so as to reduce reception operation, and immediately after the data reception, shifts to the low power consumption mode, so as to save the power.SELECTED DRAWING: Figure 1
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