A washing machine includes a tub and a drum. The tub includes a first case and a second case welded to each other; a first coupling surface extending along a circumference of the first case and facing the second case; a second coupling surface extending along a circumference of the second case and coupled to the first coupling surface; and a coupling protrusion that protrudes from the first coupling surface toward the second coupling surface and that includes a protruding end portion welded to the second coupling surface. The coupling protrusion includes: a main coupling protrusion that extends along the first coupling surface; and an auxiliary coupling protrusion that is disposed radially outward of the main coupling protrusion and spaced apart from the main coupling protrusion and that defines a discharge opening configured to discharge washing water entered between the main coupling protrusion and the auxiliary coupling protrusion.