To provide a ground unit monitoring device whereby a ground unit cab be automatically and quickly detected for whether it is normal or abnormal.

A ground unit 11, including at least one inductor L and a plurality of capacitors C1 to Cn, is laid in the vicinity of a rail 3 whether a train 4 runs. The inductor L is provided so as to be induction coupled to an on-car unit 21 provided in the train 4. A plurality of the capacitors C1 to Cn are respectively connected to the inductor L in accordance with a signal condition, thereby an LC resonance circuit of different resonance frequency is constituted. A supervisory device 12 includes a current detection means 60 detecting a resonance frequency current Ir flowing in the inductor L, a resonance frequency signal S1 supplied from the current detection means serves as one of an input condition, a decision is made whether the ground unit 11 is abnormal or normal.