A horizontal linear vibrator includes: a cover unit; a bracket providing an internal space between the cover unit and the bracket; a vibration unit including a mass body having an insertion part providing an accommodating space at one surface thereof, mounted in the internal space, and making a horizontal, linear movement; a magnetic field unit providing an electromagnetic force to allow the vibration unit to move horizontally; and one or more sub-mass units inserted in the insertion part in order to adjust a resonance frequency of the vibration unit.