An ion detection current conversion circuit includes a conversion amplifier coupled with a conversion resistor assembly for converting an ion detection current produced by an ion detector into an ion detection voltage, the conversion resistor assembly comprising a resistor having a high resistance and a capacitive compensation element, and a compensation voltage circuit for deriving a compensation voltage from the ion detection voltage and feeding the compensation voltage to the capacitive compensation element, the compensation voltage circuit comprising a variable resistor for adjusting the compensation voltage.