PURPOSE: To allow the electric resistance value to be stabilized for a long time by letting the constituent consist of polymer having the heterocyclic structure which includes >C=N+< bonding in its conductive particles and molecules, and of thermoplastic polymer.

CONSTITUTION: Polymer containing the heterocyclic structure including >C=N+< bonding in molecules used for self temperature control exothermic composition is desirably to be one having structural formula represented by formula I. In the formula, *-CH-CH-* represents principal chain or side chain of polymer, *-C-* represents principal chain of polymer, R1 and R3 represent hydrogen or substituent group respectively, and R2 represents substituent group. The content of the heterocyclic structure including >C=N+< bonding contained in polymer is normally 1 to 10 per molecule in terms of a molecular weight of polymer, and it is preferably 1 to 3. By this constitution, composition thus obtained is excellent in electric resistance stability for bending and curvature, and can generates exothermic heat uniformly.