In a joint structure for joining an insertion shaft that is driven to rotate to a reception side shaft having an insertion groove into which the insertion shaft is inserted so that a rotation of the insertion shaft is transmitted to the reception side shaft, a plurality of pairs of opposing side face portions are formed on an outer periphery of the insertion shaft, the insertion groove includes an axial hole that is formed to open onto an end surface of the reception side shaft and coincides with a pair of first side face portions of the side face portions, and a radial hole that is formed to penetrate the reception side shaft in a radial direction and coincides with a pair of second side face portions of the side face portions, and the axial hole and the radial hole are formed such that respective parts thereof intersect.