PURPOSE: To prevent static electricity generated on an object transported and maintain the specified feeding speed by supplying a humidified air bubble generated in a water trough into the space for transportation, and varying the humidity around the object.

CONSTITUTION: An air pump 11 is operated, and bubbles are produced in the water by a bubble generator 4, and now the humidity of the air in a humidifying chamber 6 is raised gradually. From a fan 5 the external air is supplied to this humidifying chamber 6, the humidity of the air is adjusted properly, and the humidified air with the humidity adjusted is flowed into the space for transportation 9 via a duct 7 by the wind pressure of the fan 5. Accordingly only the humidity of the space 9, i.e., humidity around the object transported, rises locally even though the humidity in the working room is maintained to a specified level. This prevents generation of static electricity, and the feeding speed of a supplying machine 8 can be kept at a specified value.