A lubricating oil composition comprising a base oil of lubricating viscosity having a kinematic viscosity of 22 to 300 mm2/s at 40° C. and dissolved or dispersed therein the following additives in the following amounts based on a total amount of the lubricating oil composition: (1) an overbased sulfurized alkylphenol calcium salt detergent in an amount of 0.1 to 1.6 wt. % in terms of calcium content, (2) an overbased calcium alkylbenzenesulfonate detergent in an amount of 0.6 to 2.1 wt. % in terms of calcium content, (3) a nitrogen-containing ashless dispersant in an amount of 0.005 to 0.1 wt. % in terms of nitrogen content, and (4) a zinc dihydrocarbyldithiophosphate in an amount of 0.01 to 0.1 wt. % in terms of phosphorus content, wherein the weight ratio of the overbased sulfurized alkylphenol calcium salt detergent to the overbased calcium alkylbenzenesulfonate detergent is in the range of 10:90 to 40:60 in terms of calcium content and wherein the lubricating oil composition has a total base number of 30 to 60 mg·KOH/g.