An exhaust gas temperature detection sensor is arranged at a predetermined position outside a muffler, or at a predetermined position outside an exhaust pipe constituting an exhaust gas flow passage on a more downstream side than the muffler in an exhaust direction. The sensor detects that an atmosphere temperature at the predetermined position outside the muffler has reached a predetermined temperature based on an increase in a temperature inside the muffler, or detects that an atmosphere temperature at the predetermined position outside the exhaust pipe has reached a predetermined temperature based on an increase in a temperature of an exhaust gas inside the exhaust pipe.