A hard magnetic Bi-substituted rare earth iron garnet material with excellent Faraday rotary moment, temperature property, wavelength property and insertion loss is provided. A Bi-substituted rare earth iron garnet material having a chemical composition of (Bi.sub.3-a-b-cGd.sub.aTb.sub.bYb.sub.c) Fe.sub.(5-w)M.sub.wO.sub.12 (where, M is at least one element selected from the group consisting of Ga, Al, Ge, Sc, In, Si and Ti, 0.5.ltoreq.a+b+c.ltoreq.2.5, 0.2.ltoreq.w.ltoreq.2.5) can be provided with hard magnetism and have excellent Faraday rotary moment, temperature property, wavelength property and insertion loss.