Disclosed are a lubricant composition to which is added as buffer particles to a lubricant polyurethane resin particles obtained by reacting and synthesizing long-chain polyol having a number-average molecular weight of not less than 500, a crosslinking agent having three or more active hydrogen groups in one molecule, and polyisocyanate as buffer particles, a speed reduction gear filled with the lubricant composition, and an electric power steering apparatus having the speed reduction gear incorporated therein, wherein noise produced by the speed reduction gear can be made lower than ever before irrespective of the magnitude of backlash in a case where a worm and a worm wheel are combined with each other and without complicating the configuration of the speed reduction gear by the buffer action of the buffer particles added to the lubricant composition, thereby making it possible to reduce noise produced in an automobile due to the electric power steering apparatus at low cost.