Manufacture cost and maintenance cost of RF coils of MRI devices are reduced without any limitation concerning size of the coils. By constituting an antenna device for magnetic resonance imaging devices with a cylindrical outer conductor, a looped ribbon-shaped conductor disposed inside the cylindrical outer conductor along the cylindrical surface, and a feed point for transmission and/or reception between the cylindrical conductor and the ribbon-shaped conductor, and disposing the ribbon-shaped conductor so that length thereof can be readily adjusted, there is provided an antenna device for magnetic resonance imaging devices that generates a magnetic field component perpendicular to the central axis of the cylinder at a desired resonance frequency and shows sensitivity without using capacitors and without being imposed any limitation concerning size in the diametral direction of the cylinder.