To provide a portable X-ray fluorescence analyzer which is driven by a DC power source, for which the power source is readily supplied.

A power source input part of this portable X-ray fluorescence analyzer, driven by the DC power source, includes a DC power source input terminal 1, a DC power source input terminal 2, a polarity-determining means 3 for determining the polarity of the inputted DC power source, and a polarity state display means 4 for displaying a polarity state of the inputted DC power source according to the output of the polarity-determining means 3. Moreover, a reversed connection protecting means 5 is set for preventing an input current from being fed to a load, when the DC power source is detected by the polarity- determining means 3 to be inputted with a reversed polarity. A switch means 6 is further set for switching a channel of the input current, to supply the power source of a positive polarity to the load, when the DC power source is detected by the polarity-determining means 3 to have been inputted with reversed polarity.