The present invention provides a scrubbing device retractably movable into a pipe to effectively separate caking from the pipe. The scrubber comprises a plurality of metal brush wheels or is provided with bristles. The scrubber is moved into the pipe by a flexible rod, and the rod can be retractably and automatically received in a chamber by a winding machine therein. Each of the brush wheels can be formed with a plurality of helical teeth located on the circumference thereof. The caking adhered on the inner wall of the pipe can be cleanly scrubbed away by the teeth, and then the removed caking and its ashes can be effectively expelled out of the pipe by the suction of a vacuum cleaner.