A working fluid filtering device for an electrical discharge machine, which includes a working tank comprising therein an electric discharge machining unit in which a workpiece is electrical-discharge-machined by an electrode, a contaminated fluid tank in which a working fluid from the working tank is collected and pooled, and a filter tank formed with an opening at a bottom portion thereof, wherein a filter is brought into contact with the bottom portion of the filter tank and the working fluid from the contaminated fluid tank is filled into a space defined by the filter tank and the filter and is filtered, the working fluid filtering device comprising: a filter collection roll actuator configured to rotate a filter collection roll which collects the filter; a filter supply roll actuator configured to rotate a filter supply roll which is a rolled form of the filter for working fluid filtration; characterised by further comprising a movement amount detection unit configured to detect an amount of movement of the filter; an actuator for close contact configured to bring a seal disposed on the filter tank into close contact with the filter and separate the seal from the filter; a pressure detection unit (25, 9) configured to detect a pressure of the working fluid in the filter tank; a nozzle configured to wash the filter disposed upstream or downstream relative to the filter tank; and a control unit configured to perform control such that the actuator for close contact is driven to bring the seal into close contact with the filter, the working fluid is filtered with the filter tank being sealed, and when a predetermined value is exceeded by the pressure of the working fluid detected by the pressure detection unit (25, 9), the actuator for close contact is driven to separate the seal and the filter from each other, and the filter supply roll actuator and the filter collection roll actuator are synchronously driven to move the filter a predetermined distance so that the filter is washed. a filter collection roll actuator configured to rotate a filter collection roll which collects the filter; a filter supply roll actuator configured to rotate a filter supply roll which is a rolled form of the filter for working fluid filtration; characterised by further comprising a movement amount detection unit configured to detect an amount of movement of the filter; an actuator for close contact configured to bring a seal disposed on the filter tank into close contact with the filter and separate the seal from the filter; a pressure detection unit (25, 9) configured to detect a pressure of the working fluid in the filter tank; a nozzle configured to wash the filter disposed upstream or downstream relative to the filter tank; and a control unit configured to perform control such that the actuator for close contact is driven to bring the seal into close contact with the filter, the working fluid is filtered with the filter tank being sealed, and when a predetermined value is exceeded by the pressure of the working fluid detected by the pressure detection unit (25, 9), the actuator for close contact is driven to separate the seal and the filter from each other, and the filter supply roll actuator and the filter collection roll actuator are synchronously driven to move the filter a predetermined distance so that the filter is washed.