To provide a running body capable of greatly saving fuel to be consumed by utilizing inertia force and making acceleration and deceleration dynamic movement by using a new control method.

A vehicle employs an automatic coasting device to set speed by an accelerator pedal 1, feed back running body speed by a generator or a rotary transducer 11 and other detection body, compare them in a set speed-detection speed comparison part, and operate a fuel adjusting part 6 based on the difference. Furthermore, a fuel adjustment mechanism of an engine 13 is controlled for acceleration, and an electromagnetic clutch 10 is released after reaching target speed to move to idling operation for running. When speed is reduced below allowance of target speed, the electromagnetic clutch 10 is connected to stop idling operation and switch to operation for set speed-detection speed comparison. By using feedback control, acceleration and deceleration of the running body (vehicle, marine running device, ship) are made dynamic and great reduction of fuel consumption is realized. Moreover, a noise problem and an exhaust gas problem in a city can be solved at a stroke.