A volumetric braking device includes: a brake disk having an outer surface where a plurality of disk vanes are formed with a predetermined spacing therebetween; a cylinder case where the brake disk is arranged, and the internal space of a cylinder is sectioned into a plurality of spaces by the disk vanes; a piston-drive unit, which has a piston roller sliding on the brake disk, and where the compressed pressure resistance generated between the piston roller and any one disk vane and vacuum pressure resistance generated between the piston roller and another disk vane operate as a braking load for the brake disk to perform decelerating and braking operations; a drive motor, which receives an electrical signal from an ECU by a program to operate in a forward or reverse direction; and a drive unit operating module for operating the piston-drive unit by operating the drive motor.