The influence of transverse magnetic field on surface a.c. field-effect in germanium has been studied, and a different interpretation from other inverstigators is proposed. According to our experimental results, it may be considered that the influence of magnetic field on surface field-effect is predominantly referred to the additional change in conductance of sample caused by the "magnetic-concentration effect" rather than the change in surface barrier height caused by the Hall e.m.f., and we also suggest the possibility of using this experiment to determine the dependence of the surface recombination velocity on the surface barrier.