To provide a compact portable data recorder for performing long-hour measurement/recording without enlarging the current-carrying capacity of a battery and its external form.

This data recorder is driven by using a commercial power source and a battery as power sources, and is characterized in that the energization of several circuits within the recorder is controlled correspondent to the kind of a drive power source. This data recorder includes a voltage detection circuit detecting an output voltage of a commercial power source system and a switch for separately controlling the energization of a display part, an auxiliary circuit part, and a measurement circuit part, and is characterized in that the energization is turned off of the display part and the auxiliary circuit part when no output voltage is detected in the source system while the energization of the measurement circuit part is selectively turned on in synchronization with a measurement period.

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