A lubricating oil composition for industrial gears, comprising 10 to 90% by mass of a lubricant base oil having the properties of the below to, and 90 to 10% by mass of a liquid random copolymer of ethylene and α-olefin, the liquid random copolymer being prepared by the below method (α), wherein the total amount of the lubricant base oil and the copolymer is 100% by mass, the lubricating oil composition for industrial gears having the property of the below: The lubricant base oil has a kinematic viscosity at 100°C of 1 to 100 mm 2 /s, The lubricant base oil has a viscosity index of 100 or more, The lubricant base oil has a pour point of 0°C or lower, The lubricating oil composition for industrial gears has a kinematic viscosity at 40°C of 100 to 10,000 mm 2 /s, (Method (α)) A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system comprising (a) a bridged metallocene compound represented by the 1 following Formula 1, and (b) at least one compound selected from a group consisting of (i) an organoaluminum oxy-compound, and (ii) a compound which reacts with the bridged metallocene compound to form an ion pair, wherein, in Formula 1, R 1, R 2, R 3, R 4, R 5, R 8, R 9 and R 12 are respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure, wherein R 2 or R 3 bonded to the 3-position of the cyclopentadienyl group is a n-butyl group, R 6 and R 11, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R 7 and R 10, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R 6 and R 7 are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R 11 and R 10 are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R 6, R 7, R 10 and R 11 are not hydrogen atom at the same time; Y is a carbon atom or silicon atom; R 13 and R 14 are independently aryl group; M is Ti, Zr or Hf; Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons; and j is an integer of 1 to 4. 10 to 90% by mass of a lubricant base oil having the properties of the below to, and 90 to 10% by mass of a liquid random copolymer of ethylene and α-olefin, the liquid random copolymer being prepared by the below method (α), wherein the total amount of the lubricant base oil and the copolymer is 100% by mass, the lubricating oil composition for industrial gears having the property of the below: The lubricant base oil has a kinematic viscosity at 100°C of 1 to 100 mm 2 /s, The lubricant base oil has a viscosity index of 100 or more, The lubricant base oil has a pour point of 0°C or lower, The lubricating oil composition for industrial gears has a kinematic viscosity at 40°C of 100 to 10,000 mm 2 /s, (Method (α)) The lubricant base oil has a kinematic viscosity at 100°C of 1 to 100 mm 2 /s, The lubricant base oil has a viscosity index of 100 or more, The lubricant base oil has a pour point of 0°C or lower, The lubricating oil composition for industrial gears has a kinematic viscosity at 40°C of 100 to 10,000 mm 2 /s, (Method (α)) A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system comprising (a) a bridged metallocene compound represented by the 1 following Formula 1, and (b) at least one compound selected from a group consisting of (i) an organoaluminum oxy-compound, and (ii) a compound which reacts with the bridged metallocene compound to form an ion pair, (a) a bridged metallocene compound represented by the 1 following Formula 1, and (b) at least one compound selected from a group consisting of (i) an organoaluminum oxy-compound, and (ii) a compound which reacts with the bridged metallocene compound to form an ion pair, (i) an organoaluminum oxy-compound, and (ii) a compound which reacts with the bridged metallocene compound to form an ion pair, wherein, in Formula 1, R 1, R 2, R 3, R 4, R 5, R 8, R 9 and R 12 are respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure, wherein R 2 or R 3 bonded to the 3-position of the cyclopentadienyl group is a n-butyl group, R 6 and R 11, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R 7 and R 10, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R 6 and R 7 are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R 11 and R 10 are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R 6, R 7, R 10 and R 11 are not hydrogen atom at the same time; Y is a carbon atom or silicon atom; R 13 and R 14 are independently aryl group; M is Ti, Zr or Hf; Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons; and j is an integer of 1 to 4.