The self-calibrating leak detector circuit arrangement comprises a measuring probe for generating an electrical signal when exposed to the leaking gas. A measuring amplifier is connected to the probe for amplifying the electrical signal and a second integrating amplifier stage is connected to the measuring amplifier output for amplifying the signal. The second amplifier stage has a feedback connection to the input of the measuring amplifier for counteracting at least a part of the electrical signal from the probe. A push button switch is advantageously connected between the measuring amplifier and the second amplifier stage to momentarily impress the output of the measuring amplifier on the input of the second integrating amplifier stage. Indicators are connected to the outputs of the respective amplifiers for a reading of their respective outputs.