Quantum annealing by ferromagnetic interaction is investigated for random-field Ising ferromagnets and Ising spin-glasses, using the Bethe-type mean-field annealing scheme. The fact that there are rooms of choice of the type of quantum fluctuations is a prominent feature in quantum annealing which does not exist in classical simulated annealing. Results of mean-field annealing show that quantum annealing by ferromagnetic interaction lowers the energy of the obtained approximate ground state below that by conventional quantum annealing using only transverse field.