To provide varnish for an insulator free of materials restricted by PRTR restriction such as methylbenzene and dichlormethane and capable of presenting equal or better performance compared to a conventional insulator.

Asphalt is dissolved in solvent consisting of methylcyclohexane and ethylcyclohexane or in solvent consisting of ethylcyclohexane to make up the varnish for the insulator. Preferably, for example, the solvent is 250 to 800 pts.wt. for asphalt 100 pts.wt. and the solvent consists of 60 to 100 pts.wt. of methylcyclohexane and 40 to 0 pts.wt. of ethylcyclohexane.