wherein said determination means determines whether said machine difference data needs to be obtained again at least based on: a lapsed period of time from the update time; the number of {TAIL ~ the errors} with the value not less than the predetermined value at said stop position; and the number of {HEAD ~ the transfer failures}, and 
wherein said determination means determines whether said machine difference data needs to be obtained again at least based on : a lapsed period of time from the update time ; the number of { TAIL ~ the errors } with the value not less than the predetermined value at said stop position ; and the number of { HEAD ~ the transfer failures } , and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH