PURPOSE: To improve the withstand voltage characteristic of a cathode-ray tube and improve the conditioning method for cathode-ray tube to facilitate the regulation of an apparatus using the cathode-ray tube.

CONSTITUTION: A voltage of 1V is applied to a first grid 9 at a second grid electron emitting treatment for removing an evaporated material from a cathode 8 adhered to a second grid 10, a voltage of 600-1800V is applied to the second grid 10, a voltage of -300-4000V is applied to a third grid 11, and the applied voltage to the cathode 8 is changed within the range of 0-150V. Thus, the unnecessary thermal stress to an electron gun by the second grid electron emitting treatment and an additional heating means for neck tube, the deformation, distortion, and derivation of slippage of the electrode thereby, and, in its turn, the change of focusing performance and electron emitting performance of a cathode-ray tube are suppressed.