PURPOSE: To provide an oscillating tank driving device of simple constitution with durability even if oscillating an oscillating tank almost at equal velocity.

CONSTITUTION: An oscillating tank 1 is supported by a rotatable supporting shaft 2 oscillatingly around the axis of the supporting shaft 2. A driving means 6 formed of a normal-reverse rotatable driving motor 7 and a speed reducer 8 is provided, and a driving gear 10 is fixed to the output shaft 9 of the driving means 6. A driven gear 5 is fixed to the supporting shaft 2, and a pair of intermediate gears 11 respectively meshed with the gears 10, 5 from both sides are interposed between the driving gear 10 and the driven gear 5. Position adjusting means 12 are provided to individually adjust the positions of a pair of intermediate gears 11, and the driving gear 10 and the driven gears 5 are interlocked with each other by a pair of intermediate gears 11.