An antenna comprising a split ring resonator, wherein: the antenna has a main portion, a feeding portion and a plurality of radiation elements (300E, 301E, 302E); the main portion forms a split ring; the feeding portion is provided on the main portion; the main portion has a first portion, a second portion, a third portion, a fourth portion and a fifth portion; any part of the second portion, the third portion and the fourth portion functions as a ground connecting point; each of the plurality of radiation elements extends from the main portion; only one of the plurality of radiation elements (300E, 301E, 302E) is positioned inside the split ring; all the other (301E, 302E) radiation elements are positioned outside the split ring; each of the radiation elements and the main portion are positioned on a common plane; each of the radiation elements has an extending portion and a coupling portion; the extending portion is positioned away from the main portion and extends along the third portion of the main portion; the coupling portion couples the extending portion and the main portion with each other; the main portion has a first end portion and a second end portion; the split ring has a split portion; the first end portion and the second end portion form the split portion; the antenna further has a first facing portion and a second facing portion; the first facing portion is provided on the first end portion or extends from the first end portion; the second facing portion is provided on the second end portion or extends from the second end portion; and the first facing portion and the second facing portion are spaced away from each other and face each other, wherein the first facing portion and the second facing portion constitute a capacitor. the antenna has a main portion, a feeding portion and a plurality of radiation elements (300E, 301E, 302E); the main portion forms a split ring; the feeding portion is provided on the main portion; the main portion has a first portion, a second portion, a third portion, a fourth portion and a fifth portion; any part of the second portion, the third portion and the fourth portion functions as a ground connecting point; each of the plurality of radiation elements extends from the main portion; only one of the plurality of radiation elements (300E, 301E, 302E) is positioned inside the split ring; all the other (301E, 302E) radiation elements are positioned outside the split ring; each of the radiation elements and the main portion are positioned on a common plane; each of the radiation elements has an extending portion and a coupling portion; the extending portion is positioned away from the main portion and extends along the third portion of the main portion; the coupling portion couples the extending portion and the main portion with each other; the main portion has a first end portion and a second end portion; the split ring has a split portion; the first end portion and the second end portion form the split portion; the antenna further has a first facing portion and a second facing portion; the first facing portion is provided on the first end portion or extends from the first end portion; the second facing portion is provided on the second end portion or extends from the second end portion; and the first facing portion and the second facing portion are spaced away from each other and face each other, wherein the first facing portion and the second facing portion constitute a capacitor.