DATA CARRIER

A level determination section determines the degree of need to monitor a sensor (how often monitoring should be performed) in accordance with a plurality of conditions set based on one or both of a measured quantity obtained from the sensor and the rate of change of the measured quantity, and outputs a determination signal according to the determination result. An oscillator controls the frequency of a clock signal output therefrom, in accordance with the determination signal, and supplies the clock signal to a data processing/recording section which performs data processing on the measured quantity and command information.