PURPOSE: To provide a cathode-ray tube of a long life and a high reliability in which possibility of heat wire breakage of an indirectly heated cathode is extremely low.

CONSTITUTION: An insulation coating film at an inner part comprising alumina powder is formed by a deposition method around a tungsten core wire after it is formed in a specified form of a heater of an indirectly heated cathode. In a process of forming a black insulation coating film at an outer part comprising alumina powder and tungsten powder after that, for forming a suspension liquid for applying the powder on the tungsten core wire by immersion, solution of binding agent dissolved in organic solvent is filtered using a filter having filtration performance to catch solid foreign matter of about 0.1-2μm or more. The solution from which powder dust of heavy metal such as iron is then mixed and agitated with powder of alumina and tungsten to be suspended.