A magnetic field application device according to an embodiment includes a first coil assembly and a second coil assembly spaced apart in parallel from each other, a power supply configured to apply respective currents to the first coil assembly and the second coil assembly, a controller, and a resonator accommodation unit disposed between the first coil assembly and the second coil assembly, wherein each of the first coil assembly and the second coil includes a coil configured to generate a magnetic field, a guide member connected to a terminal of the coil, a magnetic material mount connected to a terminal of the guide member, and a magnetic material fixed to the magnetic material mount, and wherein the controller is configured to control the currents applied from the power supply to the first coil assembly and the second coil assembly.