An antenna device includes an RFIC element, a power supply coil connected to the RFIC element, and a first coil conductor including a first large-diameter loop shaped conductor and a first small-diameter loop shaped conductor. The first coil conductor functions as a booster antenna and forms an antenna resonance circuit. The power supply coil is accommodated in a recess surrounded by the first small-diameter loop shaped conductor. The power supply coil is disposed in a manner that its winding direction is aligned with the winding axis direction of the first small-diameter loop shaped conductor and its outer diameter is inside a coil opening of the first small-diameter loop shaped conductor in a planar view. The power supply coil is coupled to the first small-diameter loop shaped conductor through a magnetic field.