To provide a repairing method and a repairing work preparation device, shortening a time before starting out repair of a leaking part of a steam pipe to shorten a time for the repairing work.

A repairing method includes: a steam valve closing step of closing steam valves 311, 321; an open drain valve closing step of closing flash pipe open drain valves 3311a, 3311b; a steam condenser drain valve opening step of opening steam condenser drain valves 341a, 341b; and a vacuum pump start-up step of starting up a vacuum pump 212. A repairing work preparation device 10 closes the steam valves 311, 321, closes the flash pipe open drain valves 3311a, 3311b, opens the steam condenser drain valves 341a, 341b, and starts up the vacuum pump 212. Further, the repairing work preparation device 10 opens atmosphere open drain valves 3321a, 3321b of atmosphere open drain lines 332a, 332b disposed in the vicinity of the leaking part out of the open drain lines.