A washing machine includes a cabinet in which space is formed; a tub which is formed in a cylindrical shape and is provided inside the cabinet to form a washing space in which washing water is filled; and a drum which is rotatably provided in the washing space and in which laundry is received, wherein the tub of the washing machine includes a first case and a second case which are coupled to each other to form the washing space; a first coupling surface which is formed along an entire periphery of an opened end portion of the first case and extending radially outward along the outer periphery of the first case; a second coupling surface which is formed along a periphery of an opened end portion of the second case facing the first case and extending radially outward along the outer periphery of the second case, the second coupling surface being bonded to the first coupling surface by welding; and a coupling protrusion which is formed so as to protrude in an axial direction of the tub along the first coupling surface and of which a protruding end portion is welded to the second coupling surface, and wherein the coupling protrusion includes a main-coupling protrusion which extends in a circumferential direction along the first coupling surface; and a sub-coupling protrusion which extends in parallel with the main-coupling protrusion at a position radially spaced apart from the main-coupling protrusion, characterised in that the first coupling surface has different widths extending radially according to the position, the main-coupling protrusion is formed over the entire first coupling surface, and the sub-coupling protrusion is partially formed only in a region of the first coupling surface having a width in which both the main-coupling protrusion and the sub-coupling protrusion can be formed. a first case and a second case which are coupled to each other to form the washing space; a first coupling surface which is formed along an entire periphery of an opened end portion of the first case and extending radially outward along the outer periphery of the first case; a second coupling surface which is formed along a periphery of an opened end portion of the second case facing the first case and extending radially outward along the outer periphery of the second case, the second coupling surface being bonded to the first coupling surface by welding; and a coupling protrusion which is formed so as to protrude in an axial direction of the tub along the first coupling surface and of which a protruding end portion is welded to the second coupling surface, and wherein the coupling protrusion includes a main-coupling protrusion which extends in a circumferential direction along the first coupling surface; and a sub-coupling protrusion which extends in parallel with the main-coupling protrusion at a position radially spaced apart from the main-coupling protrusion, characterised in that the first coupling surface has different widths extending radially according to the position, the main-coupling protrusion is formed over the entire first coupling surface, and the sub-coupling protrusion is partially formed only in a region of the first coupling surface having a width in which both the main-coupling protrusion and the sub-coupling protrusion can be formed.