s if the kinematic viscosity of the polyolefin oil is below 500 mm 2 s an oil film is liable to be broken in a high temperature and high humidity environment in which fine droplets are emulsified if the kinematic viscosity exceeds 1200 mm 2 s an initial decrease amount of the torque becomes large as the above described base oil the poly u03b1 olefin can be preferably used a mixture of two or more poly u03b1 olefins having different viscosities can be used to allow the base oil to have a predetermined viscosity but it is preferable to use the poly u03b1 olefin singly because the above described base oil has a high viscosity it has a high oil film forming performance therefore the above described base oil has a high effect of restraining the torque limiter from chattering and a bearing from being worn thereby lengthening the life of the bearing the base oil is excellent in chemical non attacking property more specifically when the composition of the lubricating oil leaks to the outside of the torque limiter for some reason or contacts members made of synthetic resin disposed on the periphery thereof the composition of the lubricating oil does not chemically attack them in the present invention it is possible to use an emulsifier capable of emulsifying fine droplets mixed with the synthetic saturated hydrocarbon oil in an environment having a high humidity in which dew condensates as a preferable emulsifier it is possible to use a metallic salts of sulfonic acid shown by a chemical formula 3 shown below in the chemical formula 3 reference symbol.