PURPOSE: To solve malodor of wastewater and prevent pollution by malodor by providing a grease trap for reserving kitchen wastewater with a deodorizer solution feeding machine, and intermittently injecting a deodorizer solution into the grease trap through a feed pipe.

CONSTITUTION: A grease trap 1 is formed with a rectangular pallelopided having a wastewater hole 11, baffle plates 12, and a scupper 13. The wastewater from a kitchen 2 is entered into the grease trap 1 through a wastewater injection pipe 3. A deodorizer solution feeding machine 4 is provided, and a deodorizer solution is intermittently injected into the grease trap 1 through a deodorizer solution feeding pipe 41 and an injection hole 14. As the deodorizer solution, highly commercially available liquid deodorizers such as ammonia, hydrogen sulfide, and mercaptane are used. The malodor of wastewater is solved, and the malodor at the time of cleaning the grease trap 1 is prevented from scattering around.