When this well-house was disassembled for restoration in 1969, the ridegpole bearing the note written in Indian ink "Lucky day in October, 1626", was found. From the note, it came to be known that the structure was built in 1626, and that by miracle it escaped damage from both the major fire of the Main Tower when hit by lightening in 1665 and the fire in the Honmaru (Inner Bailey) resulting from the Battles of Boshin.