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