The present invention relates to an attachment device by means of which, in use, an object is attached to a roof rack which is or at least can be connected to roof rails of a car, comprising a housing, at least two movable jaws extending to outside the housing, which jaws engage round a roof rack in use, and actuating means provided with an operating element for moving said at least two jaws together, wherein the actuating means are designed to translate the jaws and comprise at least one rack, which rack is engaged when the operating element is operated. The invention further relates to a combination of a roof rack and such an attachment device and to a combination of an object to be attached to a roof rack and such an attachment device.