A radio frequency IC device that prevents variations in the value of capacitive coupling between a radio frequency IC element and a radiation electrode and has good signal transmission efficiency includes a radio frequency IC element including input/output electrodes and, a first base including intermediate electrodes that are capacitively coupled to the input/output electrodes and have capacitance values C1a and C1b, respectively, and a second base including radiation electrodes and that are capacitively coupled to the intermediate electrodes and have capacitance values C2a and C2b, respectively. A capacitance C1 obtained by combining C1a and C1b is smaller than a capacitance C2 obtained by combining C2a and C2b.