An antenna is provided with a conductive member. The conductive member has a main part, an opposing part, a first feed terminal, and a second feed terminal. The main part extends along a horizontal plane so as to have an opened ring shape. The main part has a first end section and a second end section that are located apart from each other. The opposing part includes a first opposing part provided on the first end section and a second opposing part provided on the second end section. The first opposing part and the second opposing part are spaced apart from, and opposed to, each other. The main part has a thin part that is thinner than both the first opposing part and the second opposing part.