A nail gun includes a housing having a first locking element, an opposite second locking element, and a sliding groove, a safety mechanism including an actuation member in the sliding groove, the actuation member having an end nose, and a nail alignment adjustment mechanism including a lever pivotably secured to the housing, a spring having a first end secured to the other end of the lever and a second end affixed to the actuation member, and a spring-biased selector including a shank passing the lever, and a knob secured to the shank. Pivoting the knob from a first position to a second position will cause the nose to contact a first workpiece. Pivoting the knob from the second position to the first position will cause the nose to dispose above a second workpiece and align a nail with a through hole of the second workpiece.