A control device that controls a plurality of inverters respectively provided corresponding to a plurality of alternating-current electric motors so as to control the plurality of alternating-current electric motors by current feedback. According to the invention, the director and responder functionality are made available in a resource server of the packet network. The changes in temperature and pressure during hydrogen absorption-desorption which are characteristic of hydride storage media air is used to measure the hydrogen concentration in the storage vessel and the hydrogen to metal hydride.