A control system for a gas sensor element capable of lessening the effect of variations in sensor properties among gas sensor elements as well as the effect of environmental factors, such as temperature and humidity, to thereby accurately detect variation in the concentration of a specific gas. In a control system 10 for a gas sensor element 11 whose sensor resistance Rs varies with the concentration of NOx gas, a pulse signal Sc which alternates between 0 V and +5 V is input to a pulse input terminal 17. When a voltage of 5 V is applied to the pulse input terminal 17, a capacitor 14 is charged via a fixed resistor 15 having a resistance Rc and a diode 16. When a voltage of 0 V is applied, the capacitor 14 discharges via the gas sensor element 11. An output voltage Vout is A/D-converted and processed by means of a microcomputer 20, thereby controlling an electronic control assembly 21. The potential Vout at an operating point Pd varies with the sensor resistance Rs as well as with the duty ratio DT of the pulse signal Sc. Thus, the output voltage Vout can be maintained within a predetermined range by adjusting the duty ratio.