The following year (1953), it was designated as an important cultural property of Tokyo because although the stones used for the ceiling of the stone chamber were exposed at the time, the burial mound and the stone chamber remained and it was proved that the stone chamber has a structure called Dohari-fukushitsu-kozo (multiple rooms with a womb-like structure).
当時、石室の天井石は露出していたが、墳丘、石室が残っている事や石室が胴張複室構造である事が判明したため、翌年(1953年)、東京都指定文化財となった。