An organic semiconductor element functions as a strain sensor, and includes a substrate and an organic semiconductor layer formed on the substrate as a single-crystal thin film of an organic semiconductor that is a polycyclic aromatic compound with four or more rings or a polycyclic compound with four or more rings including one or a plurality of unsaturated five-membered heterocyclic compounds and a plurality of benzene rings. Since the organic semiconductor layer is formed as the single-crystal thin film, an identical crystal structure is obtained regardless of formation technique. Therefore, when the same strain is given, the same carrier mobility is obtained and uniform property is obtained with respect to the strain. Accordingly, it is possible to provide strain sensors having uniform property.