To attain energy-saving drive by effective use of kinetic energy of a running vehicle.

During constant speed running at a target average speed Vs, acceleration running and inertia running are repeated while controlling the acceleration a and acceleration time Ta at the acceleration running, and the acceleration i and acceleration time Ti at the inertia running of a vehicle to satisfy the following relation: aTa=iTi=2Vr (wherein Vr is permissible speed deviation for the target average speed Vs). When the target average speed Vs is increased at an acceleration , i.e. when Vs=Vs0+t (wherein Vs0 is initial value of target average speed, -ia), acceleration running and inertia running are repeated while satisfying the following relation: (a-)Ta=(i+)Ti=2Vr. In order to enhance energy saving effect, the vehicle weight m and the absolute deceleration value i at the inertia running are minimized, while the value of Vr and the acceleration time Ta are set as small as possible while satisfying the requirement of aTa or iTi.