The invention relates to a fuel-operated firing device for driving securing elements into a substrate, comprising at least one main combustion chamber for a fuel, a driving piston that can be driven out of the main combustion chamber in a firing direction by expandable gases, and a pre-chamber with which an ignition device is associated and in which a pressure acting on the main combustion chamber can build up prior to a fuel-air mixture being ignited in said main combustion chamber. In order to improve the efficacy and/or functionality during the driving in of securing elements, a valve system is associated with the pre-chamber, by which valve system a maximum charge pressure in the pre-chamber can be varied in order to adjust the firing energy provided during the firing operation.