In a hammerless automatic pistol with double-action and single-action functions there are provided between the trigger arm and firing pin of the trigger mechanism a catch pawl for the firing pin and a support lever that maintains the catch pawl in the catch position. During double-action operation, both of these intermediate components are disengaged but they are engaged for single-action function. The engagement and disengagement of these intermediate components is performed automatically during the shooting cycle. By merely removing one or both of these intermediate components the automatic pistol can be modified for double-action only trigger function, in which the firing pin is simultaneously cocked and released for firing during each shot by actuating the trigger.