To perform the continuous and efficient vacuum seam cleaning work or vacuum drying work of a cleaning object using a belt conveyor.

An upper covering body 12 covering and sealing the cleaning object 11 placed on the upper surface of the belt conveyor 1 from above is formed. A lower covering body 10 arranged on the lower surface of the belt conveyor 1 to communicate with the upper covering body 12 through a distribution hole 26 formed through the belt conveyor 1, and airtightly sealing the cleaning object 11 with the upper covering body 12 is formed. A pressure reducing mechanism 13 provided with a solvent recovering function and a steam supply mechanism 16 supplying cleaning steam into the upper covering body 12 are connected to the upper covering body 12 or the lower covering body 10. The covering bodies are vertically movable to the upper surface of the belt conveyor 1 so that the vacuum steam cleaning of the cleaning object 11 sealed and stored in the upper covering body 12 can be performed, and the cleaning object 11 can be put in and out.