A lubricating oil composition comprising a base oil containing an olefin-based polymer and optionally an ether compound represented by the following formula: R 1 -O-R 2 wherein R 1 and R 2 each independently represent an alkyl group having 6 to 22 carbon atoms, a viscosity index improver containing a comb-shaped polymer, and an organic molybdenum-based compound in an amount of 400 ppm by mass to 1000 ppm by mass, in terms of a molybdenum atom, wherein, the olefin-based polymer satisfies the following requirements to: • Requirement: An area ratio of a peak derived from a hydride of a decene trimer is 80% or more relative to 100% of a total area of peaks derived from the olefin-based polymer detected in a chromatogram on performing chromatography analysis, • Requirement: A kinematic viscosity at 40°C is 16.0 mm 2 /s or less, • Requirement: A kinematic viscosity at 100°C is from 3.0 to 4.0 mm 2 /s, • Requirement: A flash point is 220°C or higher, measured in conformity with JIS K 2265-4, COC method; and • Requirement: A pour point is -30°C or lower; the content of the comb-shaped polymer is 0.30% by mass to 3.20% by mass on the basis of the whole amount of the lubricating oil composition; the total content of the component and the component, if present, is 60% by mass to 100% by mass, based on the base oil; the content of the ether compound, if present, is 30 to 300 parts by mass based on 100 parts by mass of the olefin-based polymer; and the lubricating oil composition satisfies the following requirements to: • Requirement: A HTHS viscosity (H 150) at 150°C is 1.5 mPa·s or more, • Requirement: A HTHS viscosity (H 50) at 50°C is less than 12.3 mPa·s, and • Requirement: A NOACK value is 15.0% by mass or less. a viscosity index improver containing a comb-shaped polymer, and an organic molybdenum-based compound in an amount of 400 ppm by mass to 1000 ppm by mass, in terms of a molybdenum atom, wherein, the olefin-based polymer satisfies the following requirements to: • Requirement: An area ratio of a peak derived from a hydride of a decene trimer is 80% or more relative to 100% of a total area of peaks derived from the olefin-based polymer detected in a chromatogram on performing chromatography analysis, • Requirement: A kinematic viscosity at 40°C is 16.0 mm 2 /s or less, • Requirement: A kinematic viscosity at 100°C is from 3.0 to 4.0 mm 2 /s, • Requirement: A flash point is 220°C or higher, measured in conformity with JIS K 2265-4, COC method; and • Requirement: A pour point is -30°C or lower; • Requirement: An area ratio of a peak derived from a hydride of a decene trimer is 80% or more relative to 100% of a total area of peaks derived from the olefin-based polymer detected in a chromatogram on performing chromatography analysis, • Requirement: A kinematic viscosity at 40°C is 16.0 mm 2 /s or less, • Requirement: A kinematic viscosity at 100°C is from 3.0 to 4.0 mm 2 /s, • Requirement: A flash point is 220°C or higher, measured in conformity with JIS K 2265-4, COC method; and • Requirement: A pour point is -30°C or lower; the content of the comb-shaped polymer is 0.30% by mass to 3.20% by mass on the basis of the whole amount of the lubricating oil composition; the total content of the component and the component, if present, is 60% by mass to 100% by mass, based on the base oil; the content of the ether compound, if present, is 30 to 300 parts by mass based on 100 parts by mass of the olefin-based polymer; and the lubricating oil composition satisfies the following requirements to: • Requirement: A HTHS viscosity (H 150) at 150°C is 1.5 mPa·s or more, • Requirement: A HTHS viscosity (H 50) at 50°C is less than 12.3 mPa·s, and • Requirement: A NOACK value is 15.0% by mass or less. • Requirement: A HTHS viscosity (H 150) at 150°C is 1.5 mPa·s or more, • Requirement: A HTHS viscosity (H 50) at 50°C is less than 12.3 mPa·s, and • Requirement: A NOACK value is 15.0% by mass or less.