A magnetic coupler and reader in which a high-frequency electromagnetic field for responding and reading information is properly given to a small magnetic coupling circuit element contained or added to a sheet or plate object having a high property value such as money or securities so as to ensure adequate magnetic coupling and supply adequate electric power. A read probe (magnetic coupler) (100) has a loop antenna for generating a high-frequency electromagnetic field resonantly responding to a tank circuit in a small magnetic coupling circuit element. The loop antenna is composed of a dielectric substrate (101), a first loop antenna (102A) formed on the front surface of the dielectric substrate, a second loop antenna (102B) formed on the back surface of the dielectric substrate and in the same position as that of the first loop antenna and having the same diameter as that of the first loop antenna, and connection sections (through holes) (108, 110) for connecting the first and second loop antennas in series.
