A fastening element setting device powered by an explosive gas mixture includes a housing forming a guide cylinder for a propulsion piston which drives the fastening element into a receiving material. The components of the gas mixture, one at a higher pressure than the other, are delivered through separate supply lines into an inlet duct and then to a combustion chamber. A control slide valve is located between the supply lines and the inlet duct and regulates flow, with the higher pressure component following the lower pressure component into the inlet duct and combustion chamber. A closure valve in the supply line of the lower pressure component blocks any inflow when the higher pressure component flows into the inlet duct.