A parking brake actuator includes a motor, a power transfer assembly or gearing connected to an output shaft of the motor, a planetary gear set including a linear gear connected to the power transfer assembly, a planetary gear engaged with the linear gear, and a ring gear engaged with the planetary gear and including an insertion protrusion formed on a bottom, and a housing including a motor seating recess in which the motor is accommodated and a ring gear seating in which the ring gear is accommodated, in which the ring gear accommodating portion includes an insertion groove formed on a bottom surface into which the insertion protrusion is forcibly inserted.