A lubricating oil composition comprising: a lubricating base oil having a kinematic viscosity at 100°C of 1 to 10 mm 2 /s; and 0.1 to 50 % by mass of a branched poly(meth)acrylate viscosity index improver containing a structural unit represented by the following formula in the proportion of 30 to 90 mol% and having a branching degree of 0.1 to 8.0: wherein R 1 represents hydrogen or a methyl group, and R 2 represents a linear or branched hydrocarbon group having a carbon number of 6 or less, wherein the term degree of branching means the ratio of the number of carbon atoms derived from a monomer that forms the main chain, which is the longest atom chain in the molecule, to the number of carbon atoms derived from a monomer that forms an arm branched therefrom, wherein the degree of branching is calculated as the number of carbon atoms in arm portion/the number of carbon atoms that form the main chain, wherein the viscosity index improver is a viscosity index improver having a PSSI of 5 or less and a ratio of a weight average molecular weight to the PSSI (Mw/PSSI) of 2 × 10 4 or more, wherein the term PSSI means a permanent shear stability index in accordance with ASTM D 6022-01 calculated based on the data measured in accordance with ASTM D 6278-02, wherein the weight average molecular weight is the weight average molecular weight in terms of polystyrene measured by using an HLC-8220 GPC apparatus made by Tosoh Corporation having 3 TSKgel Super MultiPore HZ-M columns made by Tosoh Corporation (4.6 mm ID × 15 cm) in series and tetrahydrofuran as a solvent at a temperature of 40°C, a flow rate of 0.35 mL/min, a sample concentration of 1% by mass, an amount of sample injection of 5 μL with a detector deference refractive index meter. a lubricating base oil having a kinematic viscosity at 100°C of 1 to 10 mm 2 /s; and 0.1 to 50 % by mass of a branched poly(meth)acrylate viscosity index improver containing a structural unit represented by the following formula in the proportion of 30 to 90 mol% and having a branching degree of 0.1 to 8.0: wherein R 1 represents hydrogen or a methyl group, and R 2 represents a linear or branched hydrocarbon group having a carbon number of 6 or less, wherein the term degree of branching means the ratio of the number of carbon atoms derived from a monomer that forms the main chain, which is the longest atom chain in the molecule, to the number of carbon atoms derived from a monomer that forms an arm branched therefrom, wherein the degree of branching is calculated as the number of carbon atoms in arm portion/the number of carbon atoms that form the main chain, wherein the viscosity index improver is a viscosity index improver having a PSSI of 5 or less and a ratio of a weight average molecular weight to the PSSI (Mw/PSSI) of 2 × 10 4 or more, wherein the term PSSI means a permanent shear stability index in accordance with ASTM D 6022-01 calculated based on the data measured in accordance with ASTM D 6278-02, wherein the weight average molecular weight is the weight average molecular weight in terms of polystyrene measured by using an HLC-8220 GPC apparatus made by Tosoh Corporation having 3 TSKgel Super MultiPore HZ-M columns made by Tosoh Corporation (4.6 mm ID × 15 cm) in series and tetrahydrofuran as a solvent at a temperature of 40°C, a flow rate of 0.35 mL/min, a sample concentration of 1% by mass, an amount of sample injection of 5 μL with a detector deference refractive index meter.