Provided is an antenna coil capable of forming a magnetic field in a desired direction in an efficient manner, while suppressing leakage of magnetic flux into a space other than the space in which the magnetic field is formed. The antenna coil includes a main coil portion formed by winding a length of conductor wire around a first reference axis and an auxiliary coil portion formed by winding the conductor wire around a second reference axis. The second reference axis is set to intersect the magnetic flux of the main coil portion at an axial end of the auxiliary coil portion. The main coil portion and the auxiliary coil portion are connected to together form a closed circuit.