The invention provides a lubricant composition for an eccentrically oscillating speed reducer of planetary gear type, which is capable of extending the life of the speed reducer under high temperatures and keeping low input torque at low temperatures, and includes (a) a base oil containing a synthetic oil, (b) a hydrocarbon wax, and (c) at least one calcium salt selected from the group consisting of a calcium salt of petroleum sulfonic acid, a calcium salt of alkyl aromatic sulfonic acid, a calcium salt of oxidized wax, an overbasic calcium salt of petroleum sulfonic acid, an overbasic calcium salt of alkyl aromatic sulfonic acid, and an overbasic calcium salt of oxidized wax.