a thermistor is used as a temperature sensor 43 in this embodiment the thermistor detects temperature of the secondary coil 41 and the corresponding detected temperature values are received by the controller not shown however since the thermistor is not turned off even though the detected temperature is above a predetermined value it is preferable to use the thermistor along with one or more other components which function as a temperature responsive safety device e g a fuse as indicated above fig5 is an enlarged perspective view of a high voltage transformer in which a secondary coil part according to a secondary embodiment of the present invention is installed on a printed circuit board pcb while fig6 is an enlarged cross sectional view of the secondary coil part taken generally line vi u2014 vi of fig5 this embodiment is similar to that described above and hence description of parts which correspond to those in the high voltage transformer according to the first embodiment of the present invention will be dispensed with or only briefly made reference to the high voltage transformer 20 of fig5 includes a pair of cores 21 and 23 and primary and secondary coil parts 60 and 70 between the coil parts 60 and 70 is installed an insulation member or micasheet 27 made of suitable insulating material a temperature sensor 80 for detecting temperature of a secondary coil 71 see fig6 in order to protect the secondary circuit is installed in the secondary coil part 70 the secondary coil 71 of the secondary coil part 70 has an annular or ring shape and as shown in fig6 an.