A resonance suppression device, in which power loss and apparatus capacitance are reduced by outputting a compensating current only while a voltage resonance is being generated, and which suppresses resonance generated by connection of a power apparatus to a power system. In one embodiment, the device includes a capacitance change detector that detects a change of an electrostatic capacitance (impedance) connected to the power system. When the resonance detector detects the resonance, a current command value generator generates the current command value on the basis of harmonic components included in a current supplied from the power apparatus to the power system. When the impedance change detector detects a change of the impedance, the current command value generator generates the current command value so as to reduce the compensating current.