Abstract: The present invention relates to an adjusting apparatus of a trigger of a pneumatic nailer comprising a gun body whose trigger assembly includes a primary trigger and a secondary trigger. A safety inflection arm presses against the secondary trigger. At least two coupled shaft holes are formed on the respective side plates of the primary trigger while a neck is interposed between the two shaft holes. An adjusting assembly composed by a shaft, a compression spring and a press block is pivotably connected to the secondary trigger so that the adjusting assembly is movable between the two shaft holes and the relative position between the secondary trigger and the safety inflection arm is rapidly adjustable.