A pipe cutter comprises a disc knife set and a roller set disposed inside a main body, a driving assembly piercing through the main body and connected to the roller set with a rotating operation component disposed on the exterior of the main body, and a conversion module connecting the main body, driving assembly, and roller set which converts the rotation of the rotating operation component into the linear movement of the roller set to adjust the relative distance between the roller set and the disc knife of the disc knife set and thereby to adapt the pipe cutter to the cutting of metal pipes with different diameters.