A speed hump device for discouraging vehicles form exceeding a designed threshold speed is disclosed. The speed hump device mainly comprises: a housing device, whose figure is like a box, having a housing room therein and a opening thereon; a hump device with a hump member and a arc-shaped member pivoted on the housing device by a first pivot, the hump member can be rotated in and out the housing room from the opening about the first pivot; a transmission device including a gear set, a transmitting mechanism and a abutment member, wherein the arc-shaped member is engaged with one gear of the gear set; a rebound device used to push the hump member out the housing device when no extra force presses on the hump member. When a car passing through the speed hump device with a slow speed, e.g., below a threshold speed, the abutment member will be put down and the hump member can be depressed in the housing room by the wheels of the car, hence the hump member as a jolt will disappear and the car will traverse smoothly; on the contrary, if the speed of the car is over the threshold speed, the hump member will be still in the position out the housing room that a jolt will occur to cause a impact effect to the car. Additionally, the hump member of the speed hump device will have an impedimental effect to a car goes against the traffic flow direction. Moreover, it does not consume any additional energy to drive the speed hump device.