A rotatable seesaw device comprises a seesaw lever arm supported by an upstanding supporting structure through a pivotal arrangement in such a manner that rotating motion about the upstanding support structure can be produced as force in peripheral direction is applied and that seesaw motion can be produced by exerting force in vertical direction. The upstanding support structure is detachable and the height thereof can be adjusted to various users such as children or adults. Further, the middle portion of the seesaw lever arm is provided with a plurality of mounting holes spaced along its length and the seesaw lever arm can be supported by the upstanding support structure at selected one of the plurality of mounting holes in order to balance the loading of different weights on opposite ends of the seesaw lever arm, thus the seesaw device can be adapted to be used by persons of different weights. With such arrangement, particularly when force including components in vertical direction and in peripheral direction is applied, rotating motion and seesaw motion can be simultaneously effected to provide a complex, resultant waveform motion around the upstanding support structure, which gives satisfactory thrill and amusement to the users.