The invention relates to a cooling device, which comprises a cooling fan and a heatsink. The heatsink is directly attached to the heating element to absorb its heat and the cooling fan is disposed on top of the heatsink to dissipate the heat. The heatsink includes a central heat dissipation body and a plurality of fins extending from the periphery of the central heat dissipation body. The central heat dissipation body has a fully-sealed hollow chamber filled with a cooling liquid and disposed an agitator. The agitator is disposed a magnetic element, and where the magnetic element corresponds to the rotor of the cooling fan must have a magnetically-attracting and mutually-dragging device in operation. By way of the magnetic attraction between the rotor of the cooling fan and the agitator, a better heat dissipation effect is secured, the chamber remains a fully-sealed room, and the cooling liquid overflow issue can be ruled out accordingly.