To provide a tool for preventing wastewater capable of preventing the wastewater from leaking from a gap between a toilet bowl body and a toilet seat of a western style toilet.

The tool for preventing wastewater from leaking capable of preventing the wastewater from leaking from a gap between the toilet bowl body and the toilet seat of the western style toilet is characterized in that the tool for preventing wastewater from leaking comprises a belt-like wastewater receiving part for receiving wastewater and a mounting part for detachably securing the wastewater receiving part to the toilet bowl body, and a gap part for discharging wastewater is formed between the wastewater receiving part and the toilet bowl body.