This paper proposes a planar monopole antenna with a parabolic edge shape. This antenna, which has notch characteristics in the wireless local area network (WLAN) band, can be miniaturized. To obtain the notch characteristics in the WLAN band, a slot with a parabolic edge shape identical to that of the monopole structure was implemented. Because the planar monopole antenna with a parabolic edge shape possesses characteristics similar to those in self-complementary structure conditions, it can be miniaturized by reducing the antenna components at the same proportion. For the antenna fabrication, an FR4 dielectric substrate with a dielectric constant of 4.7 was used. The size of the miniaturized antenna that satisfies the ultra-wide band requirement was 15.6 × 18.6 mm2, and the 10-dB band was 3.013–12.515 GHz. At each frequency, the radiation pattern was similar to that of a dipole antenna.