An antenna (20D, 20E) having a split ring resonator, wherein: the antenna comprises a first conductor and a second conductor which form, at least in part, a short stub (22D, 22E) which has a predetermined electrical length (Le); the first conductor and the second conductor form a transmission line extending over the predetermined electrical length; the antenna further comprises a third conductor and a feeding portion; each of the first conductor, the second conductor and the third conductor has a first end portion (222, 232, 242) and a second end portion (224, 234, 244); the first end portion of the first conductor is connected to the first end portion of the third conductor; the first end portion of the second conductor is connected to the second end portion of the third conductor; the second conductor and the third conductor form a split ring; the second end portion of the second conductor and the first end portion of the third conductor are located apart from each other to form a split portion of the split ring; and the feeding portion is provided to the second conductor or the third conductor, characterized in that the antenna further comprises a fourth conductor which connects the first conductor and the second conductor to each other at the second end portion of the first conductor or a vicinity of the second end portion of the first conductor; the first conductor, the second conductor and the fourth conductor form the short stub; the predetermined electrical length is equal to or more than 0.75 times a wavelength of any one of the operating frequencies; and the antenna has a plurality of operating frequencies, wherein: the short stub (22D, 22E) and the split ring as a whole form the split ring resonator; the split ring resonator operates as an LC resonator which is formed of a capacitor formed of the short stub (22D, 22E), another capacitor formed of the split ring and an inductor formed of the split ring; and the short stub (22D, 22E) operates inductively or capacitively in accordance with the frequency of an input power supplied thereto. the antenna comprises a first conductor and a second conductor which form, at least in part, a short stub (22D, 22E) which has a predetermined electrical length (Le); the first conductor and the second conductor form a transmission line extending over the predetermined electrical length; the antenna further comprises a third conductor and a feeding portion; each of the first conductor, the second conductor and the third conductor has a first end portion (222, 232, 242) and a second end portion (224, 234, 244); the first end portion of the first conductor is connected to the first end portion of the third conductor; the first end portion of the second conductor is connected to the second end portion of the third conductor; the second conductor and the third conductor form a split ring; the second end portion of the second conductor and the first end portion of the third conductor are located apart from each other to form a split portion of the split ring; and the feeding portion is provided to the second conductor or the third conductor, characterized in that the antenna further comprises a fourth conductor which connects the first conductor and the second conductor to each other at the second end portion of the first conductor or a vicinity of the second end portion of the first conductor; the first conductor, the second conductor and the fourth conductor form the short stub; the predetermined electrical length is equal to or more than 0.75 times a wavelength of any one of the operating frequencies; and the antenna has a plurality of operating frequencies, wherein: the short stub (22D, 22E) and the split ring as a whole form the split ring resonator; the split ring resonator operates as an LC resonator which is formed of a capacitor formed of the short stub (22D, 22E), another capacitor formed of the split ring and an inductor formed of the split ring; and the short stub (22D, 22E) operates inductively or capacitively in accordance with the frequency of an input power supplied thereto. the short stub (22D, 22E) and the split ring as a whole form the split ring resonator; the split ring resonator operates as an LC resonator which is formed of a capacitor formed of the short stub (22D, 22E), another capacitor formed of the split ring and an inductor formed of the split ring; and the short stub (22D, 22E) operates inductively or capacitively in accordance with the frequency of an input power supplied thereto.