PURPOSE: To lengthen life of a heater in order to improve productivity as well as to reduce cost by increasing in form of lapse of time, electric power to be supplied to a heater for heating a metal to be vacuum evaporated.

CONSTITUTION: When preparing a resistance heating heater 2 inside of vacuum chamber 1, placing a metal chip to be vacuum evaporated on said heater and forming a metal film on a phosphor screen 5 of a cathode-ray tube 4 by electrifying and heating the heater 2, electric power to be suppled to the heater 2 is made to have the voltage V1 at the moment T0 when starting vacuum evaporation, thereafter the voltage is raised up to V2 at the moment T1 while shutting it at the moment T2 or a feed quantity of electricity is continuously increased from the moment T0 to the moment T1 in order to perform vacuum evaporation thereby. In this way, life of the heater can be lengthened while improving productivity and also reducing cost.