Protective device for LC filter

A protective device protects an LC filter in a vehicle. The vehicle includes a first vehicle-mounted electric device (10) and a second vehicle-mounted electric device (40). The first vehicle-mounted electric device (10) includes a first power converter (16). The second vehicle-mounted electric device (40) includes a second power converter (19) and shares a power supply (13) with the first vehicle-mounted electric device (10). The LC filter (17) is arranged between the first power converter (16) and the power supply (13). The LC filter (17) is configured such that the resonance frequency band of the LC filter (17) can be changed. The resonance frequency band of the LC filter (17) is changed based on a ripple amount in a current flowing in the LC filter (17).