A YIG device comprises a resonator including a YIG element 16 of a single crystalline yttrium iron garnet having a part of yttrium substituted with gadolinium, which is formed in a spherical shape, and magnetic field applying means 20 for applying a magnetic field to the YIG element 16 to resonate the YIG element, whereby the YIG device can have a small ΔH and a large threshold electric power for generating the resonance saturation.