A working fluid comprising a base material and a modified silicone oil having a polar group, wherein the base material is selected from glycols selected from monoethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol with n = 4 or more; glycol ethers selected from diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, polyethylene glycol monomethyl ether with n = 5 or more, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, polyethylene glycol monoethyl ether with n = 5 or more, diethylene glycol monopropyl ether, triethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, polyethylene glycol monopropyl ether with n = 5 or more, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, polyethylene glycol monobutyl ether with n = 5 or more, triethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, polypropylene glycol monobutyl ether, and polypropylene glycol monopropyl ether, which may be used alone or two or more of the foregoing may be combined and used; and borate esters of triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, polyethylene glycol monomethyl ether with n = 5 or more, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, and polyethylene glycol monobutyl ether with n = 5 or more, which may be used alone or two or more of the foregoing may be combined and used, the modified silicone oil has a polyether group being a polar group, and another polar group other than the polyether group, said other polar group being an amino group, epoxy group, methacrylic group, mercapto group, or carboxyl group, and the content of the modified silicone oil having a polar group is 0.002 to 1.0 percent by weight. glycols selected from monoethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol with n = 4 or more; glycol ethers selected from diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, polyethylene glycol monomethyl ether with n = 5 or more, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, polyethylene glycol monoethyl ether with n = 5 or more, diethylene glycol monopropyl ether, triethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, polyethylene glycol monopropyl ether with n = 5 or more, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, polyethylene glycol monobutyl ether with n = 5 or more, triethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, polypropylene glycol monobutyl ether, and polypropylene glycol monopropyl ether, which may be used alone or two or more of the foregoing may be combined and used; and borate esters of triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, polyethylene glycol monomethyl ether with n = 5 or more, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, and polyethylene glycol monobutyl ether with n = 5 or more, which may be used alone or two or more of the foregoing may be combined and used,