A high-voltage pulse generator producing pulses with a stable flat top is described. It is based on a multistage amplitude discriminator with inductance coils. The generator produces pulses with an amplitude of up to −20 kV, a top width of up to 200 μs, and a pulse repetition rate of up to 50 Hz at a 20-kΩ load. The top width voltage instability does not exceed ±20 V. The generator is used in the power supply system of the INR linac H− injector-based ion source.