PURPOSE: To improve braking force by connecting an electromagnetic clutch, switching a changeover valve, and rotating the braking gear of a flywheel to a direction opposite to the rotation direction of an engine with an exhaust turbine driven by an exhaust gas flowed into a bypass tube.

CONSTITUTION: The turning-on condition of a switch 24 causes the ON condition of an electromagnetic clutch 21 with a controller 26, and the switching of changeover valves 22 and 23 to broken line positions respectively to discharge the exhaust gas of an engine 10 to atmosphere through a bypass tube 18 and a muffler 32. An exhaust turbine 19 is made high speed rotation by exhaust gas energy when the exhaust gas passes the bypass tube 18. A reaction force gear 16 is forced to rotate in a opposite direction (broken line arrow direction) to the rotation direction of the engine 10 by the rotational drive force via the clutch 21. This exhaust gas energy causes the action of braking force on a flywheel 12, and the lowering of the rotation of the engine 10 to decelerate a vehicle speed. This can obtain high braking force.