Abstract: A vibrating unit having a table driven by two oppositely-rotating vibration generators arranged in parallel. Each vibration generator has coaxial first and second eccentric mass shafts which are relatively rotatable between a first position producing no vibration and a second position where vibration is produced. First and second driving systems respectively include a first double-toothed drive belt drivingly engaged with each of the first shafts to effect counterrotation thereof, and a second double-toothed belt drivingly engaged with each of the second shafts to effect counterrotation thereof. A position adjusting assembly is associated with one of the driving system for permitting the eccentric mass shafts associated therewith to be angularly adjusted relative to the eccentric mass shafts of the other driving system during rotational driving of the vibration generators to permit the vibration generators to be adjusted between a vibration-producing position and a nonvibrating position.