X-ray apparatus

An X-ray apparatus comprising:

• an X-ray tube including:
• a cathode for emitting electrons when heated by a heater,
• a target for generating X-rays when bombarded by the electrons emitted from said cathode, and
• a focus electrode for maintaining a ground potential and for focusing the electrons emitted from said cathode so that the electrons bombard said target;
• and
• a control circuit for changing a cathode voltage to be applied to said cathode and a target voltage to be applied to said target, the cathode voltage and target voltage being changed based on an interlocking relationship to maintain a constant ratio of cathode voltage to target voltage, whereby the cathode and target voltages are changed on negative and positive sides of the ground potential of said focus electrode in an interlocked manner, respectively.