In an antenna device, when an AM/FM antenna as a first antenna and an SDARS antenna or a GPS antenna as a second antenna that have different frequency bands are provided in a common case, an additional conductor portion extends out from a conductor main body portion of a capacitive element, and the additional conductor portion includes a parallel strip-shaped portion having a length that is ¼ of an effective wavelength in a frequency band of the second antenna, and extending parallel to the conductor main body portion.