PURPOSE: To improve mounting work of a drain valve, prevent it from coming off and protect it from splashing, tipping or the like.

CONSTITUTION: Outside a duct body 2 where a drainage hole 8 is formed, the drainage hole 8 and its axial center are made to coincide with each other to bring a lead valve type drain valve 4 into contact, and a protector 3 which also serves as a retainer fitted on the outside periphery of the drain valve 4 is fixed on a duct body 2 by a rivet 14 to tighten the drain valve 4 against the duct body 2 for fixing. In the protector 3 which also serves as the retainer, a splash guard 13 which covers a part of outside periphery of the drain valve 4 is formed integratedly at least.