The invention relates to the technical field of engines, in particular to a shafting frequency modulator and an engine. The shafting frequency modulator comprises a housing, an inertial ring, a location pin, an elastic part and a cover plate, wherein the housing is mounted at the front end of a crankshaft; one side of the housing is provided with a ring-shaped mounting slot for accommodating the inertial ring; the inertial ring is arranged in the ring-shaped mounting slot, and is capable of generating relative sliding along the ring-shaped mounting slot; one end of the location pin is connected to the outer side of the inertial ring through the elastic part; a pin hole for allowing the location pin to insert is formed in the inner wall of the ring-shaped mounting slot; and the cover plate is encapsulated above the ring-shaped mounting slot. The shafting frequency modulator can enable the engine to have relatively high shafting frequency during working at a relatively low rotation speed, and to have relatively low shafting frequency during working at a relatively high rotation speed, so that a resonant rotation speed is avoided, and therefore, torsion vibration of the engine is at relatively low level, and the purpose of reducing the shafting torsion vibration is realized.