A variable resistor is constructed to reliably seal the space between a rotor and a substrate without insert-molding the substrate into a case, and to be produced at a very low cost. This variable resistor includes a hollow square-prism shaped case which is open at the top and the bottom, a substrate which is fitted into the lower opening of the case, and on the top surface of which a collector electrode and an arcuate resistor are provided, a rotor rotatably fitted into the upper opening of the case, a slider mounted on the bottom surface of the rotor and making sliding contact with the collector electrode and the resistor, an annular packing member disposed between the rotor and the substrate for sealing the space therebetween, terminals mounted on the substrate and electrically connected to the resistor and the collector electrode, and a metallic cover.