Provided is a covering material, which includes a backing having an upper surface and a lower surface opposite to the upper surface, and a viscoelastic layer formed on the upper surface of the backing, in which the covering material is a covering material for covering a rectangular electric wire, and an adhesive force of the viscoelastic layer to the lower surface of the backing as measured by peeling at a peeling angle of 180° and a tensile rate of 300 mm/min is 0.05 N/20 mm or more and 10 N/20 mm or less. A covered rectangular electric wire includes the covering material and a rectangular electric wire covered with the covering material. An electrical device is produced by using the covered rectangular electric wire.