To smoothly filter a processing liquid without enlarging a device in a processing liquid treating device connected to a processing device using the processing liquid in processing, and filtering the used processing liquid.

This processing liquid treating device is composed of a liquid waste tank 11 for storing a liquid waste used as the processing liquid, and an outflow passage 12 for allowing the liquid waste in the liquid waste tank 11 to flow out. The liquid waste tank 11 has a liquid waste introducing part 16 for allowing the liquid waste to flow in, a precipitation part 17 for precipitating processing chips included in the liquid waste, and a liquid waste outflow part 18 for introducing filtered water filtered by the precipitation part to the outflow passage 12. The precipitation part 17 filters the liquid waste by precipitating the processing chips by soaking a corrugated board structure 20 slantingly provided with a plurality of capillaries 20b reaching an upper part from a bottom part of the precipitation part 17.