Abstract: An object of the present invention is to provide a cathodluminescent apparatus, which is capable of adjusting brightness and which is less expensive and economical, and a phosphor powder for the same. The apparatus comprises: a line electron gun having a line cathode and an intermediate electrode, which is capable of extracting electrons from the line cathode, of linearly focusing electrons extracted and of reciprocatively scanning electrons focused; an anode for accelerating electrons emitted from the line electron gun, the anode having an electric conductive section formed on a substrate; a phosphor screen being made of phosphor particles on the electric conductive section; and a container being evacuated to a vacuum for cathodluminescence. The phosphor powder suitably used for the above-described cathodluminescent apparatus should be composed of primary particles of Y.sub.2 O.sub.2 S polycrystal which are almost spherical with their surfaces formed rough.