Cathode ray tube device of preheated type

In a cathode ray tube device including a cathode ray tube having a tube with a faceplate, an electron gun assembly including first and second grids and a cathode from which an electron beam is emitted and operating means including an anode and deflecting means for allowing the electron beam to scan the faceplate in a normal operating state of the device, and an electric circuit for driving said operating means, including a heater power source for heating the cathode in the normal operating state of the device and a waiting state of the device where the electron beam does not scan the faceplate, the improvement which comprises introducing means for introducing the electron beam from the cathode without scanning the faceplate by the electron beam while the device is kept in the waiting state and wherein the cathode ray tube consists of a fiber optics cathode ray tube including a fluorescent surface on the faceplate on one side of an optical fiber bundle and the cathode has an electron emissive layer made of oxide layer emitting a beam current of 5 to 100 mA/cm.sup.2 density.