An antenna and a wireless IC device that includes the antenna are provided for which the manufacturing process is simple and for which there is a low probability of a poor connection occurring between a feeder portion and a radiation electrode. An antenna includes a radiation electrode that is provided on a main surface of an insulator board, a ground electrode and/or a counter electrode that is arranged so as to oppose the radiation electrode, and a magnetic field electrode that is connected to the radiation electrode through a connection portion. The magnetic field electrode is defined by line-shaped electrodes and feeds a signal to the radiation electrode from a feeder portion defined by ends of the line-shaped electrodes through the magnetic field electrode.