It is a hachiryokyo (eight-lobed bronze mirror) and designated as a national treasure; the standing statue of Senju Kannon with kenzoku (one's family and relations) are carved with tagane (chisel) on the mirror side, and on the back side of the mirror, Hosoge-mon (flower motif) is carved in the center as well as butterflies and birds in four directions.
鏡面にタガネで千手観音の立像と侍立する眷属を彫り、背面には中央に宝相華文、四方に蝶や鳥を配した図柄の八稜鏡であり、国宝に指定されている。