PURPOSE: To hold the sufficient degree of vacuum while minimizing the friction and wear of rubber coated rollers contacting a wall surface to provide safe running by providing a rectangular flexible vacuum chamber constituted of the lower surface of a pair of front and rear rubber coated rollers and the lower surfaces of left and right endless rubber belts.

CONSTITUTION: Rubber coated rollers 2 slide air tightly to front and rear end plates or roof plate of a rectangular box body 1 and have respectively small diameter portions provided with chain wheels over which endless rubber belts 7 are fitted at the left and right ends. An air exhaust pipe 13 opens at the lower end to the roof plate of the box body 1 while the upper end of the pipe 13 is connected to a vacuum apparatus through a flexible hose and others. Air in a rectangular space surrounded by a pair of front and rear rubber coated rollers and a pair of endless rubber belts is discharged through the air exhaust pipe 13 by the vacuum apparatus. Thus the rectangular space serves as a vacuum chamber which moves on the outer wall of a contaminated structure is to be cleaned while being attached closely to the outer wall to remove dust and dirt with a brush 9.