Patent ID: 8911029

Claim:
An electric braking device comprising: a cylinder part that retains thereinside a piston movable in an axial direction; a motor for driving the piston; and a driving force transmission mechanism that transfers driving force by the motor to the piston, the electric braking device producing brake fluid pressure by driving the piston in the axial direction with the driving force by the motor, the driving force transmission mechanism comprising: a nut that is rotated upon reception of rotational driving force by the motor; and a screw which is engaged with the nut in a movable condition in the axial direction and which abuts the piston, the electric braking device further comprising a worn-out reducer for reducing a worn-out of a contact part between the screw and the piston, and a regulator which is disposed on an outer circumference of the piston to regulate a displacement of the piston in a radial direction, wherein the worn-out reducer is configured by an abutting face of the piston with the screw; wherein said abutting face of the piston is formed in a flat shape, and a tip portion of the screw facing the face of the piston is formed in a convex curved shape, and wherein the tip portion of the screw forms a part of a sphere, and a curvature radius of a spherical surface of the tip portion of the screw is set to be larger than a diameter of a portion of the screw near the tip portion of the screw.