A planar antenna able to secure a wide frequency band and having high reliability. Therefore, the planar antenna has at least a grounding plate, a radiating conductor, a matching portion, a power supply portion, a spacer, a central conductor and a coaxial connector. The matching portion is a flat plate having a taper shape (an inverse taper shape) narrowed in width from the power supply portion to the radiating conductor. Further, the matching portion is slantingly arranged with respect to the grounding plate.