A motor-driven machine tool comprises a tool driven in a rotating fashion, a drive shaft driven by a drive unit and an output shaft for holding the tool, wherein the rotating motion of the drive shaft can be transferred to the output shaft by way of an eccentric coupling device. A mass balancing device is provided for smoothing out vibrations, said device comprising a stroking mass part moveably mounted in a carriage guide and impinged by an eccentric member driven by one of the shafts. The stroking mass part executes a rotary smoothing motion.