A broadband circularly polarization antenna device includes: a dielectric body, a patch, an antenna feed pin, and a grounding layer. The patch is disposed on a top surface of the dielectric body. The antenna feed pin is extended outward from a bottom surface of the dielectric body. One part of the grounding layer is coated on the bottom surface of the dielectric body, and the other part of the grounding layer is coated entirely around a lateral side of the dielectric body. Because the grounding layer is coated on the bottom surface and the lateral side of the dielectric body, the bandwidth of the antenna device is increased and interference from a PCB and other surrounding circuits to the antenna device is greatly reduced, thereby ensuring the antenna device performs well.