A dielectric working fluid processor for processing dielectric working fluid used in a wire electrical discharge machine includes: a dirty liquid tank for storing dielectric working fluid containing machining swarf; a filter for removing machining swarf from the dielectric working fluid in the dirty liquid tank; a clean liquid tank for storing the dielectric working fluid from which the machining swarf has been removed by the filter; a pump for supplying dielectric working fluid from the dirty liquid tank to the filter; an inverter for controlling electric power to be supplied to the pump; a pump controller for controlling the rotation speed of the pump by varying the frequency of electric power supplied from the inverter to the pump; and a feed pressure obtainer for obtaining the feed pressure of the dielectric working fluid supplied from the pump to the filter, based on the frequency of the electric power.