Abstract: A caulking gun has a built-in cutter being formed between a handle (14) and a trigger (18) for cutting off a tip (34) of a caulking spout (36). The cutter has a cutting blade (62) being mounted in the handle and a cutting forwarder (40) for pushing the spout to the blade for cutting. One end of the cutting forwarder together with a tension spring (46) is pivoted in the trigger and another end reclines against the handle. A blade slot (60) on the top of the forwarder covers the blade for finger protection. A pair of openings (54, 55) are located in the two side wells of the blade slot of the forwarder for receiving the spout from either right side or left side of the caulking gun for cutting. The surfaces of the openings force a spout inside the openings to the blade with an angle less than 90.degree. for smoothly spout cutting while the trigger is squeezed.