Concurrently with the operation that the energizing information reception log recorder 204 updates the reception log for each serial number, based on the reception log for each adapter 100, the energizing state log recorder 205 in the remote monitoring server 200 determines an energizing state indicating whether or not power is supplied to the socket 20 connected to the adapter 100 (i.e., whether or not the socket 20 is turned on or off). Based on the determination result, the energizing state log recorder 205 repeats updating the energizing state log for each adapter 100 stored in the database 210 at S16.

Regarding this operation, more specifically, based on FIG. 9B, when the energizing state log recorder 205 receives the energizing information from the adapter 100, the energizing state log recorder 205 determines that the energizing state is “on”. After receiving the energizing information, when a threshold time T elapses without further receiving next energizing information, the energizing state log recorder 205 determines that the energizing state is “off”. The energizing state log recorder 205 repeats this determination process to output determination results. The change in determination results over time is recorded and updated as the energizing state log. Here, the threshold time T may be set to a time interval, which is obtained by adding a margin to the transmission interval set for each adapter 100 (illustrated in FIG. 4B).