Disc brake and planetary gear reduction mechanism

A disc brake comprising:

• a pair of pads each disposed on both sides of an axial direction of a rotor interposed therebetween;
• a piston configured to push at least one of the pair of pads against the rotor;
• a caliper body including a cylinder in which the piston is movably accommodated;
• a motor provided on the caliper body;
• a planetary gear reducer configured to boost and transmit rotation from the motor;
• and
• a piston propeller configured to propel the piston to a braking position by rotation transmitted thereto from the planetary gear reducer,
• wherein the planetary gear reducer includes:
• a sun gear including an input gear to which the rotation from the motor is transmitted and an output gear extending axially from a radial central region of the input gear;
• a plurality of planetary gears arranged to mesh with the output gear of the sun gear and surround the output gear;
• and
• an internal gear arranged to mesh with each planetary gear and surround the planetary gear, and
• wherein the internal gear includes:
• an internal gear body including an inner teeth that meshes with gears of the plurality of planetary gears;
• an annular wall extending from an axial end of the internal gear body toward a radial center side to restrict movement of each planetary gear in an axial direction;
• and
• a support formed in a cylindrical shape and configured to rotatably support the sun gear and extend from an inner peripheral side end of the annular wall toward a direction of being away from the internal gear body in an axial direction of the sun gear, and
• wherein the support contacts the sun gear on an outer periphery of the cylindrical shape.