A display apparatus for displaying pictures virtually instantaneously adopts a direct-heating type cathode of an impregnated structure, and includes a cathode ray tube having a dispenser cathode wherein a cathode material is filled in pores of a porous body and a porous heater is directly connected to the cathode material. A voltage generator of the apparatus produces a first voltage for driving the heater. A video signal supply portion supplies a video signal to the cathode, while a deflector deflects horizontally and vertically an electron beam generated from the cathode to produce a raster by scanning the fluorescent surface of the cathode ray tube. A flyback transformer generates a second voltage to be supplied to the anode and one or more grids of the cathode ray tube using a horizontal deflection output signal supplied from the deflector. With the described arrangement, an electron-emitting velocity of an electron gun reaches its maximum value within about one second after power is applied. Thus, the display apparatus can be adapted to an HDTV requiring high current density electron-emitting characteristics.