A muffling chamber (5) is located between a first main body wall (42A) and a second main body wall (42B) with respect to a height direction (AE). An outflow pipe (8) has: a first opening (8A) that connects an outflow passage (8R) with a muffling chamber (5) in the vicinity of a first main body wall (42A); and a second opening (8C) that connects the outflow passage (8R) with the muffling chamber (5) in the vicinity of a second main body wall (42B). The liquid staying on the first main body wall (42A) of a first muffler (4A) flows into the outflow passage (8R) through the first opening (8A). The liquid staying on a second main body wall (42B) of a second muffler (4B) flows into the outflow passage (8R) through a second opening (8C). Therefore, the symmetry of the first muffler (4A) and the second muffler (4B) is compatible with anti-corrosion.