PURPOSE: To efficiently separate paint sludge by a dehydrator without bringing about trouble such as an offensive smell problem in an apparatus removing the coating mist in the exhaust air discharged from the coating booth of coating equipment.

CONSTITUTION: A washing means bringing the exhaust gas containing coating mist in a coating booth 1 and mist collecting soln. to a contact state so as to catch the coating mist in the exhaust gas by the mist collecting soln. to discharge them to lower exhaust space 4 is installed and, further, the separation tank 2 receiving the soln. from the washing means and a dispersing means holding coating sludge to a dispersed state are arranged. A dehydrator 3 for separating the soln. in the separation tank 2 into a liquid component and the coating sludge is formed and a liquid supply means supplying the soln. in the separation tank 2 to the dehydrator 3 and also supplying the same as the mist collecting soln. is constituted by forming a low conc. soln. supply means supplying the soln. in the separation tank 2 as the mist collecting soln. while the concn. of the sludge in the soln. is kept as it is and a high conc. soln. supply means supplying the soln. in the separation tank 2 while concentrating the solid of the soln.