Strain gauges made of nickel foil are used for measuring the elastic surface stress of a specimen subjected to repeated loads. The nickel foil, about 10μm thick, is composed of crystal grains of 30μm in mean diameter. The foil is stuck on the surface of the specimen, and the elastic stress is measured by observing slip-bands in the crystal grains resulting from repeated strains. The calibration curves of the foil, i.e., the relations between the proper stress at which slip-bands begin to appear and the number of stress cycles are obtained by rotating-bending tests of (0.14)×106 cycles and at several test temperatures up to 350°C. The relation between the appearance of slip-bands and the magnitude of cyclic stress is also investigated. Applying the methods using the proper stress and the proper number of cycles which are derived from the calibration curves of the foil gauge, the peak stresses in grooved shafts under bending are measured.