To provide a configuration in which a base-isolation pad can be easily installed at a proper position and a sufficient base-isolation function using the base-isolation pad can be presented by installing the base-isolation pad at a proper position.

According to a base-isolation method of a gravestone 1, while using a base-isolation pad 16 installed between an upper base 13 and a headstone 14, and an installation instrument 20 including a base on which the base-isolation pad is placed, a regulation part 22 erected from an end portion of the base and a placement part which is provided in the base while being spaced apart from the regulation part at a predetermined interval, the regulation part of the installation instrument is abutted to a side face 14c of the headstone 14, the base-isolation pad 16 is deposited to a bottom face 14b of the headstone, and the headstone is piled up on a top face 13a of the upper base which is positioned on the lower side.