A vibration apparatus for a molding box which enlarges the range in which a vibrating force can be increased and decreased. In the apparatus, a first gear pulley 16 for rotating a first rotary shaft having a first eccentric weight fixed thereto and a second gear pulley 17 for rotating a second rotary shaft having a second eccentric weight fixed thereto are disposed on the same plane, and similar third and fourth rotary shafts are disposed immediately below the first and second rotary shafts, respectively. An endless timing belt 37 is passed around a prime mover gear pulley 33 and a gear pulley 36 disposed on a slidable base 31 capable of horizontal displacement in such a manner as to extend from the lower side of the first gear pulley 16 to the upper side of the second gear pulley 17 and from the upper side of the fourth gear pulley 19 to the lower side of the third gear pulley 18, and the slidable base 31 can thus move in a direction parallel to the timing-belt 37.