Abstract: An electric heating apparatus comprises a sheet heating element having two end electrodes and a center electrode. The sheet heating element is wound around the external peripheral surface of an airtight and elastic expandable balloon. The balloon is disposed inside a lining material impregnated with a thermosetting resin for repairing a pipe and is swelled against the inside wall of the pipe through the lining material. The end and center electrodes are supplied with electricity to generate heat in the sheet heating element, thereby curing the thermosetting resin impregnated in the lining material. This allows pipe lining to be performed with much higher energy efficiency and simpler steps.