The electric parking brake actuator has a built-in DC motor. When the motor operates, the motor's speed is reduced by the 2 step worm gear reducer and a ball screw mechanism, increasing torque. The 2nd worm wheel gear turns the spindle and the nut inside the caliper piston forcing it outward to generate brake pad clamping force. The electric parking brake actuators are automatically adjusted to compensate for brake pad wear, so no parking brake adjustment is necessary.