Lubricant composition for a speed reducer, and speed reducer

A lubricant composition for an eccentric oscillating planetary gear type speed reducer, consisting of the following components (a) to (e):

• (a) a base oil containing a synthetic oil;
• (b) at least one calcium salt selected from the group consisting of calcium salts of petroleum sulfonic acids, calcium salts of alkyl aromatic sulfonic acids, calcium salts of salicylates, calcium salts of phenates, calcium salts of oxidized waxes, overbased calcium salts of petroleum sulfonic acids, overbased calcium salts of alkyl aromatic sulfonic acids, overbased calcium salts of salicylates, overbased calcium salts of phenates, and overbased calcium salts of oxidized waxes;
• (c) an antioxidant;
• (d) a glycerin fatty acid ester;
• and
• (e) an optional additive selected from the group consisting of metal salt rust inhibitors other than the component (b), metal salt detergent-dispersants other than the component (b), antioxidants other than the component (c), metal corrosion inhibitors, antiwear agents, extreme pressure agents, and solid lubricants other than the component (d).