PURPOSE: To most efficiently remove an extraneous substance, by inclining the neck of a cathode-ray tube downward to make the maximum deflection angle side of the funnel portion of the tube nearly vertical, and imparting an impact to the tube while rotating it.

CONSTITUTION: The neck 1b of a cathode-ray tube 1 is inclined downward at an angle of about 20W45° to make the maximum deflection angle side of the funnel portion 1a of the tube nearly vertical. A tapping impact 2 or the like is imparted to the side of the tube 1 while it is rotated. As a result, an extraneous substance is effectively dropped along the funnel portion 1a. Since the impact is uniformly applied to the entire side of the tube 1, the extraneous substance is most effectively removed.