A switching power supply determines the order n of the power supply higher harmonic component near the receiving frequency fc of an AM radio broadcast, and judges whether the higher harmonic component of the order n is higher or lower than the receiving frequency fc of the AM radio broadcast. More specifically, a bandwidth usage rate is calculated from a bandwidth allocated in a updating period and a bandwidth actually used in the updating period. The wafer supports are secured within the enclosure portion rigidly at the bottom margin and resiliently at the top margin.