A vehicle including a floor tunnel (60, 260) and a sub-muffler (1, 201) having a polygonal shape in cross section, the sub-muffler (1, 201) being connected to an inflow pipe (3, 51, 203) and a discharging pipe (3, 52) and being housed in the floor tunnel (60, 260) extending in a longitudinal direction of the vehicle and providing a space formed between a wall surface (62, 63, 64, 65, 66, 67, 262, 263, 264, 265, 266) forming the floor tunnel (60, 260) and an outer surface of a main body (20, 220) of the sub-muffler (1, 201), the floor tunnel (60, 260) including an inclined surface (63, 64, 65, 67, 263, 265) inclined with respect to the road surface at a certain angle in the front/back direction of the sub-muffler (1, 201), the sub-muffler (1, 201) comprising: a main body (20, 220) having a polygonal outer shape in cross section in a continuous fashion over its length in a longitudinal direction; a first end part (21, 221) extending on a side of an inflow pipe, a cross sectional area of the first end part becoming smaller toward one side thereof in the longitudinal direction of the main body (20, 220), the inflow pipe being configured to feed exhaust into the main body; and a second end part (22, 222) extending on a side of a discharging pipe, a cross sectional area of the second end part becoming smaller toward the other side thereof in the longitudinal direction of the main body (20, 220), the discharging pipe being configured to discharge the exhaust from the main body (20, 220), wherein the outer shape of the main body (20, 220) is shaped so as to conform to a shape of a wall surface (62, 63, 64, 65, 66, 67, 262, 263, 264, 265, 266) forming the floor tunnel (60, 260) and to have a surface roughly conforming to the inclined surface (63, 64, 65, 67, 263, 265) of the floor tunnel (60, 260), and hence when the main body (20, 220) is housed in the floor tunnel (60, 260), the space formed between the wall surface (62, 63, 64, 65, 66, 67, 262, 263, 264, 265, 266) and the outer surface of the main body (20, 220) is occupied by the main body so as to leave only a predetermined clearance therebetween, and the main body (20, 220) and the first and second end parts (21, 22, 221, 222) are formed from one plate raw material. a main body (20, 220) having a polygonal outer shape in cross section in a continuous fashion over its length in a longitudinal direction; a first end part (21, 221) extending on a side of an inflow pipe, a cross sectional area of the first end part becoming smaller toward one side thereof in the longitudinal direction of the main body (20, 220), the inflow pipe being configured to feed exhaust into the main body; and a second end part (22, 222) extending on a side of a discharging pipe, a cross sectional area of the second end part becoming smaller toward the other side thereof in the longitudinal direction of the main body (20, 220), the discharging pipe being configured to discharge the exhaust from the main body (20, 220), wherein the outer shape of the main body (20, 220) is shaped so as to conform to a shape of a wall surface (62, 63, 64, 65, 66, 67, 262, 263, 264, 265, 266) forming the floor tunnel (60, 260) and to have a surface roughly conforming to the inclined surface (63, 64, 65, 67, 263, 265) of the floor tunnel (60, 260), and hence when the main body (20, 220) is housed in the floor tunnel (60, 260), the space formed between the wall surface (62, 63, 64, 65, 66, 67, 262, 263, 264, 265, 266) and the outer surface of the main body (20, 220) is occupied by the main body so as to leave only a predetermined clearance therebetween, and the main body (20, 220) and the first and second end parts (21, 22, 221, 222) are formed from one plate raw material.