A strain gauge includes a substrate formed of resin and having flexibility and a functional layer formed of a metal, an alloy, or a metal compound, directly on one surface of the substrate. The strain gauge includes a resistor formed as a film that contains Cr, CrN, and Cr2N and into which an element contained in the functional layer is diffused. The resistor is provided on one surface of the functional layer. A first substance having a function of controlling growth of crystal grains as a main component of the resistor, is added to the resistor.