A new attachment structure for an antenna unit includes a gasket that prevents entry of water and is configured to have an improved external appearance. An antenna unit includes an antenna module which receives radio waves transmitted from a satellite and a cover member which has inner space large enough to house the antenna module. The cover member has an opened bottom surface which joins with a bottom plate that closes the opened bottom surface of the cover member. A gasket covers at least a periphery of the bottom plate. The gasket comes into contact with the inner surface of the cover member to seal the inner space. Because the gasket does not have a cover portion which covers the outer surface of the cover member, the problem of reduced waterproofed quality when the cover portion is pulled can be prevented, while also providing a fine appearance.