A mold oscillator includes: a ball screw unit that has a ball screw 32having a threaded shaft 29 and a ball nut 30, and a nut-side shaft 31 fixed to the ball nut 30 coaxially with the threaded shaft 29, wherein the ball screw unit is positioned so that the central axis of the ball screw unit extends in the vertical direction; and a power transmitting mechanism that transmits rotation to the ball screw unit. Bearings rotatably support a first shaft. A second shaft that is the other of the threaded shaft and the nut-side shaft is connected to the mold side. An attachment portion to fix the mold oscillator at an installation position is provided so as to be immovable relative to the bearings in the vertical direction and is configured to be able to change the relative position between the bearings and the second shall in the vertical direction in a state where operation of the mold oscillator is stopped.