A screw tightening structure includes an indented concave recess formed on a screw, and mating convex sections provided on a screw tightening tool for tightening the screw: the recess and the mating convex sections including three or more torque transfer portions, respectively, which protrude outward and are disposed at equiangular intervals for concentrically mating engagements; rotating the screw tightening tool causing the torque transfer portions of the mating convex sections to transfer a tightening torque to the screw via the torque transfer portions of the recess; under which outer circumferential edge portions of the torque transfer portions of the mating convex sections to be brought into abutting contact with sidewall of the torque transfer portions of the recess with the tightening torque being transferred to the screw via force application points Q representing resulting abutment portions.