To solve the problem that a drain plug for opening and closing a drain port of a wash bowl, a wash-hand basin or the like is apt to be pulled out and lost since it can be easily pulled out of the drain port.

When the drain plug is opened and closed, an elastic engaging claw of an engaging member mounted on a supporting part of the drain plug is movable up and down in an overflow port formed in the drain port, and is locked at the edge of the overflow port preventing it from being pulled out of the drain port, so that the drain plug implement can be prevented being lost or stolen.