A puncture assisting tool for assisting in a puncturing operation by a puncture tool that is used to insert and place a spacer between bones and includes an arc-shaped needle includes a base section configured to be in contact with a skin of a patient; and a guide unit configured to be fixed with respect to the base section. The guide unit has a curvature that is approximately the same as a curvature of an arc shape of the puncture tool. The guide unit is configured such that an outer arc-shaped surface of the puncture tool can be placed in contact with the guide unit to guide the puncture tool in an arc trajectory while the puncture tool is being inserted into the patient.