An apparatus to generate a high voltage includes an outputting part having a power transforming part formed with a primary and a secondary coil, a switching part to control an output voltage induced in the secondary coil of the power transforming part, by interrupting a current in the primary coil of the power transforming part, a digital controlling part to control an interruption operation of the switching part according to a time constant determining a wave form of the output voltage of the power transforming part and a control reference value determining a level of the output voltage, and a digital interfacing part to convert input control data having first and second forms into the time constant and the control reference value, respectively, and to provide the time constant and the control reference value to the digital controlling part.