A urea-based lubricating grease composition comprising (a) as a thickener, a diurea compound which is an alkyldiurea compound having an average molecular weight in the range of from 600 to 700, wherein in the range of from 25 to 60 mole % of the total alkyl groups is an unsaturated component, and the total amine value of the primary amine constituting the raw material is in the range of from 250 to 350, (b) a base oil having as its main component one or more synthetic hydrocarbon oil(s) having a pour point of -40°C or below, wherein the kinematic viscosity of the base oil is 6000 mm2/sec or less at -40°C, and (c) as additives, a mixture comprising an oil-soluble organic molybdenum complex, an oil-soluble organic zinc compound of dithiocarbamic acid, an oil-soluble organic zinc compound of dithiophosphoric acid and an inorganic sulphur compound; and a roller bearing and electric power steering device wherein the said lubricating grease composition is used as the lubricant.