To prevent the overcharge of a storage device, to secure sufficient braking force during deceleration by preventing the breakage of a main brake device due to its overheat or a lack of its braking force, and to sufficiently improve fuel economy.

During decelerating travel, the capacity of a hydraulic motor for a HST is kept larger or the capacity of a hydraulic pump is kept smaller than during other travel (S6), and the kinetic energy of a vehicle is regenerated via the HST in this condition. During decelerating travel when the storage amount of the storage device is smaller than a set value, the regenerated energy is used for operating a generator/motor as a generator to generate power (S11). The generated power is stored in the storage device, and if an auxiliary brake device is being operated at this time, the braking force of the auxiliary brake device is reduced or turned off depending on an increase of the power generation quantity (S8). During decelerating travel when the storage amount of the storage device is greater than the set value, the power generating operation of the generator/motor with the regenerated energy is turned off (S13), and the auxiliary brake device is operated (S12).