Magnetic marker installation method and supplemental tool for installing magnetic marker

A supplemental tool for installing a magnetic marker for arranging, when the magnetic marker externally acting with magnetism is installed, the magnetic marker in an accommodation hole provided by being drilled in a road surface, the supplemental tool for installation comprising:

• a columnar-shaped retaining member including a retaining surface for the magnetic marker at an end portion in an axial direction of the retaining member;
• a detaching member to be combined with the retaining member that is movable in the axial direction with respect to the retaining member;
• and
• a measuring member including a grounding portion facing the road surface,
• wherein, in a combination of the retaining member and the detaching member, the detaching member is positioned in contact with the magnetic marker retained on the retaining surface, and the retaining member is configured to retreat in the axial direction from the magnetic marker while keeping a state in which the detaching member is in contact with the magnetic marker,
• wherein an insertion depth of the retaining member into the accommodation hole is measured or checked in accordance with a relative position in a height direction between the retaining member inserted into the accommodation hole and the measuring member with the grounding portion in contact with the road surface.