The present invention provided an antenna which has a band usable for UWB and which is small and thin with 50% bandwidth. In the antenna to be used for UWB communication in 3 to 5 GHz frequency, a taper slot 11 is formed in a rectangular conductive plate 10, a vertical slit 12 for separating the conductive pate 10 is formed at the top of the taper slot 11, a feeding point part 13 and a grounding point part 14 are formed at the conductive plate 10 and on both sides of the vertical slit 12, and the lower slits 15 are formed on the oblique sides 11a, 11a of the taper slot 11 near the feeding point part 13 and the grounding point part 14.