A speed reduction mechanism includes: a speed reduction unit that includes an input member formed of an external gear that makes circular motion about a rotation axis with an eccentric amount, and a rotation force applying member formed of an internal gear that is in mesh with the input member; and a lubricating oil supply unit that supplies lubricating oil to a bearing of the speed reduction unit. The lubricating oil supply unit includes an oil tank arranged outside of the rotation force applying member, an oil delivery passage that delivers the lubricating oil to the oil tank, and a first oil introduction passage that introduces the lubricating oil from the oil tank to the bearing. The lubricating oil is delivered to the oil delivery passage through pumping action of the input member based on the circular motion.