To easily travel even in a narrow place in self-advancing to a work site by shortening the whole length of a self-advancing conveyor apparatus with longitudinally extensible constitution at a conveyor part.

This self-advancing conveyor apparatus is provided with an undercarriage 1 allowing self-advance, and conveyor part 8 provided at the upper part of the undercarriage. The conveyor part 8 comprises an upper stage conveyor 12, a middle stage conveyor 13 and a lower stage conveyor 14 arranged in three vertical stages. The upper stage conveyor 12 and lower stage conveyor 14 are longitudinally slid so as to be longitudinally extensible at the conveyor part 8.