In an antenna device having a substantially conical conductive member, having upper and lower sides made open, erected in a substantially vertical direction around a substantially circular microstrip patch provided on the upper side of a substantially circular substrate, the lower opening portion of the conductive member is grounded to a ground plate provided on the lower side of the substrate, and the diameter of the upper opening portion of the conductive member is larger than the diameter of the lower opening portion of the conductive member.