The pyrochlore molybdate Gd2Mo2O7 locates near the phase boundary between the ferromagnetic-metallic and the spin-glass insulating state. This metal-insulator transition is governed on a large energy scale by the electron-correlation effect, while the geometrical frustration causes the random potential. The magnetic field can tune the randomness of the potential and control, under a suitable pressure, the continuous Mott-Anderson transition precisely. The critical exponent (mu=1.04 +/- 0.1) of the Mott-Anderson transition has been determined for this ferromagnetic orbital-degenerate electron system.