Using the hydrogen abstraction reaction of triplet benzophenone with triethylgermane in an SDS micellar solution, we succeeded in enriching Ge-73 with the magnetic isotope effect. At zero magnetic field, 0.5% enrichment of Ge-73 was observed for the cage product (diphenyl(triethylgermyl)methanol). With increasing magnetic field strength (B), the enrichment of Ge-73 increased initially, attaining the maximum value of 5.3% at 500 G. At higher fields (500 G < B less than or equal to 10 kG), it decreased gradually, becoming 1.0% at 10 kG. The magnetic field dependence of the enrichment of Ge-73 can be explained by the relaxation mechanism.