A strain gauge includes a flexible substrate and a functional layer formed of a metal, an alloy, or a metal compound, the functional layer being directly on one surface of the substrate. The strain gauge includes a resistor formed of a film that includes Cr, CrN, and Cr2N and that is formed with α-Cr as a main component. The functional layer includes a function of promoting crystal growth of α-Cr and forming an α-Cr based film.