A hole plug for waste water includes a protruding portion having a flange with a dish shape, and a drain hole therein; and a cylindrical portion projecting from the protruding portion and formed at an inner face side of the flange, the cylindrical portion being configured to be inserted into and pass through an attachment hole of a panel. The cylindrical portion includes an engagement leg provided in a circumference configured to detachably engage the attachment hole, a cylinder inside, and a shielding wall which is positioned above the drain hole, is larger than a horizontal cross-sectional surface of the drain hole, and is provided such that the cylinder inside and the drain hole can communicate with each other for allowing a liquid entering into an inside of a vehicle to flow into the cylinder inside and flow out to an outside of a vehicle from the drain hole.