An antenna (100, 100A) mountable on an object, wherein: the antenna has a main portion, a facing portion (300, 300A), a first feed terminal, a second feed terminal and at least one reinforcing terminal (600, 600A); the main portion has a ring shape which includes a split line portion; the split line portion extends in a predetermined direction; the split line portion has a split, a first end portion and a second end portion; the first end portion and the second end portion are positioned away from each other in the predetermined direction with the split left therebetween; the facing portion includes a first facing portion (320, 320A) and a second facing portion (340, 340A); the first facing portion is provided on the first end portion; the second facing portion is provided on the second end portion; the first facing portion and the second facing portion are spaced away from each other and face each other; each of the first feed terminal and the second feed terminal is provided on the main portion; each of the first feed terminal and the second feed terminal is configured to be fixed to the object when the antenna is mounted on the object; the at least one reinforcing terminal is positioned away from the split line portion; the at least one reinforcing terminal extends from the facing portion; and the at least one reinforcing terminal is configured to be fixed to the object when the antenna is mounted on the object, wherein the antenna forms a split ring resonator, wherein the facing portion constitutes a capacitor of the antenna, the main portion constitutes an inductance of the antenna and the facing portion and the main portion form an LC resonator circuit. the antenna has a main portion, a facing portion (300, 300A), a first feed terminal, a second feed terminal and at least one reinforcing terminal (600, 600A); the main portion has a ring shape which includes a split line portion; the split line portion extends in a predetermined direction; the split line portion has a split, a first end portion and a second end portion; the first end portion and the second end portion are positioned away from each other in the predetermined direction with the split left therebetween; the facing portion includes a first facing portion (320, 320A) and a second facing portion (340, 340A); the first facing portion is provided on the first end portion; the second facing portion is provided on the second end portion; the first facing portion and the second facing portion are spaced away from each other and face each other; each of the first feed terminal and the second feed terminal is provided on the main portion; each of the first feed terminal and the second feed terminal is configured to be fixed to the object when the antenna is mounted on the object; the at least one reinforcing terminal is positioned away from the split line portion; the at least one reinforcing terminal extends from the facing portion; and the at least one reinforcing terminal is configured to be fixed to the object when the antenna is mounted on the object, wherein the antenna forms a split ring resonator, wherein the facing portion constitutes a capacitor of the antenna, the main portion constitutes an inductance of the antenna and the facing portion and the main portion form an LC resonator circuit.