PURPOSE: To provide a protective sheet difficult to peel even at a high temperature when a conductor connecting section is insulated and protected through oscillatory-wave welding.

CONSTITUTION: In a protective sheet 10, in which a low melting-point material layer 10b is formed onto the surface of a high melting-point material layer 10a, a large number of projections 11 are formed to the surface of the high melting-point material layer 10a, and the low melting-point material layer 10b is formed onto said surface of the layer 10a so that the tips of the projections 11 are exposed. The protective sheet 10 is used for forming a molded insulating layer by pressing and holding the conductor connecting sections of insulated covered wires l, 2 and insulated covered layers in the vicinity of the conductor connecting sections from both upper and lower surfaces while directing the low melting-point material layer 10b side toward the inside and melting the low melting-point material layer 10b by oscillatory waves under the state.