Abstract: A piston braking device for a hydraulic or pneumatic cylinder, employing an annular braking plate loosely fitted on the piston rod of the cylinder and rockable into a tilted position relative to the piston rod upon actuation by a plate drive means, and a brake control mechanism operative to apply a counter pressure on the braking plate to maintain or reset the braking plate in a normal right angle position, the braking plate having braking portions on its inner periphery which braking portions are pressed against the circumference of the piston rod to apply friction brakes thereto in a manner which increases the braking force in proportion to the propelling force of the piston rod.