To provide a flexible heating element and its manufacturing method capable of easily satisfying both of a folding property when it is not used, and a shape restoring property when it is used by using a heating element with stable electric resistance in a length direction.

The flexible heating element is formed by arranging a shape memory alloy wire, which is subjected to shape memory treatment in a predetermined shape, in a base material 2. The shape memory alloy wire in the base material is transformed from an austenitic phase to a martensite phase when the flexible heating element is not used, and the flexible heating element is folded in a state that a longitudinal elastic coefficient is reduced than a value when it is used. When the flexible heating element is used, the shape memory alloy wire in the base material is heated to a temperature higher than a reverse transformation completion temperature by Joule heat, and plastic deformation by folding given in the martensite phase is eliminated when the alloy wire is transformed into the austenitic phase to return to an original shape. The flexible heating element is manufactured by arranging the shape memory alloy wire after the shape memory treatment in the base material having an electronic insulation property after the shape memory treatment by heating to a shape memory treatment temperature in a state that the shape memory alloy wire is maintained in a predetermined shape.