to make a microcomputer not shown performing other functions of the display apparatus carry out the function of this comparison circuit 19 fig3 is a block diagram showing a structure of a third example of the crt display apparatus according to the invention in fig3 the elements that are the same as those in fig1 are given the same reference numerals and explanation thereof will be omitted the third example differs from the first example in that the comparison circuit 19 is supplied with the output voltage of the g 2 electrode voltage source 16 instead of the output voltage of the gm electrode voltage source 17 that is in the third example the voltage at the high tension level feedback point 9 and the output voltage of the g 2 electrode voltage source 16 are input into the comparison circuit 19 in a case where although the output voltage of the g 2 electrode voltage source is at a normal value only the voltage at the high tension level feedback point 9 falls from its normal value the comparison circuit 19 determines that a discharge has occurred between any electrode within the electron gun and the anode or the cathode and delivers a signal indicative of occurrence of the discharge in response to this signal the high tension control circuit 22 reduces the.