To provide a muffler device capable of improving the discharge of exhaust gas, while discharging the exhaust gas in any desired direction. The muffler device is connected to a rear end portion of an exhaust pipe extending from an internal combustion engine of a vehicle. An exhaust outlet opening is provided that opens outwardly and laterally of the vehicle and is disposed at a rear portion of a muffler main body. The muffler main body is provided with a muffler side cover and an end cap as muffler covers. The muffler side cover includes a slit. The slit serves as an air intake guide shaped portion for guiding ambient air so that the ambient air crosses the exhaust outlet.