To suppress formation and accumulation of spatial electric changes and enhance the dielectric breakdown characteristic by furnishing an insulative substance layer which consists of synthesized polylefin or a bridged structure from it and whose moisture content lies under a specified level.

A DC cable concerned includes a conductor 1 consisting of copper strands. On this conductor 1, a semiconductive polyethylene composition is extruded as covering so that an internal semiconductive layer 2 is formed. The obtained semiconductive layer 2 is covered by an extrusion process with an insulative composition prepartred by mixing a bridging agent and age resistor with a polyethylene material synthesized through the action of metallocene catalyst, followed by a bridging process with heat so that an insulative substance layer 3 is formed. This layer 3 is covered by the extrusion process with a semiconductive polyethylene compound the same as used in the above-mentioned semiconductive layer 2 so that an external semiconductive layer 4 is formed, and further thereover a soft polyvinyl chloride resin is extruded as covering so that a sheath 5 is accomplished. After bridging, the insulative substance layer 3 is left on a vacuum so that its water content becomes under 10ppm.