A pneumatic nailer includes a working piston connected to a driving plunger for driving in a fastening means and which is subjected to compressed air when a driving-in process is triggered. The nailer also includes a triggering device which has a manually actuatable trigger and a contact feeler. Actuating the trigger and the contact feeler together activates a first control valve and can trigger a driving-in process. A second control valve is activated when actuating the trigger independently of an actuation of the contact feeler. A chamber is provided, which is either aerated or deaerated via a throttle when the second control valve is activated. A locking piston is provided which is displaced from a resting position into a locked position when the pressure in the chamber passes a predetermined pressure threshold and which in the locked position prevents a driving-in process from being triggered.