To provide a novel lubricant composition which neither rises in consistency nor separates the lubricating base oil nor leaks the separated lubricating base oil even when repeatedly stressed over a long period, a reduction gear using the above lubricant composition, and an electric power steering device.

The lubricant composition uses at least two types of combined thickening agents including lithium stearate as a thickening agent and has a worked penetration (25°C) of 355 or more. The reduction gear 50 is filled with the above lubricant composition containing fine particles. The electric power steering system comprises the above reduction gear.