To develop a strain sensor used to safety monitor various type structures by sensing a ground subsidence of a steel structure, a reinforced concrete structure or the like or a strain due to an earthquake.

The strain sensor is made of a conductive particle-polymer of a linear or sheet state in which the conductive particles are dispersed in the polymer and the polymer is made of a thermoplastic elastomer. Here, the elastomer is a block copolymer of two or more ingredients. Particularly, the copolymer is preferred to be a styrene - diene block copolymer or a hydrogen- added styrene - diene block copolymer. More particularly, there is a styrene - butadiene block copolymer or styrene - isoprene block copolymer which is hydrogen-added.