PURPOSE: To provide an evenly distributed composition by putting a predetermined amount of carbon black in crystalline polyethylene having specific MFR, and preventing destruction of the carbon black during kneading.

CONSTITUTION: Polyethylene is employed as matrix and its degree of crystallization is selected within the range of 60 to 95% and MFR is limited to 1-25g/10min so as to prevent distribution of carbon black from becoming uneven. The carbon black employed is hard to be destructed during kneading if it has a relatively large grain size, a small specific surface area and a structure that absorbs oil by a small amount. The use of a structure cross-linked by electron beams can heigten to a significant level the mechanical strength and heat resistance which are weak points of polyethylene of high fluidity. The carbon black is evenly distributed so that dispersion of the self-temperature control performance of the heating element is prevented.