PURPOSE: To improve workability by installing an expansion lifting frame on rails vertically laid on an inclined face via a removable fixing device and horizontally fitting a lengthy working table on the lifting frame via horizontal adjusting mechanisms.

CONSTITUTION: A worker (a) operates a working equipment 15 on the footboard 10a of a lengthy working table 10 and horizontally performs the work on the inclined face 1. The fixing with rails 3 by a removable fixing device 4b is released, a hydraulic cylinder 6 is extended, an upper lifting frame 5b is extended upward, and the lifting frame 5b is fixed to the rails by the fixing device 4b. The fixing with the rails 3 by a removable fixing device 4a is released, the cylinder 6 is shrunk, a lower lifting frame 5a is lifted and fixed to the rails 3 by the fixing device 4a, and the working table 10 is lifted by one step. The working table 10 is horizontally adjusted by horizontal adjusting mechanisms 8 and 9, and the work is performed with the working equipment 15.