To provide a method which enables sectional stress of an expansion lock bolt to be measured by installing a strain gauge in the expansion lock bolt without causing damage to the strain gauge.

In this method for measuring the sectional stress of the expansion lock bolt, the strain gauges 2a and 2b are fixed in prescribed positions on a prescribed cross section of a rod-like member 1 by adjusting sensitivity to the axial direction, in such a manner that the sensitivity direction of the strain gauges 2a and 2b corresponds to the axial direction of the lock bolt 5; a rod-like strain detection unit is formed by providing an output member 3 for guiding electrical output, and is fixed to the inside of the lock bolt 5 by means of an injected solidification agent; the strain gauges 2a and 2b are subjected to strain by following expansion and contraction strain caused by the stress of the lock bolt 5; and an electric current corresponding to the strain occurring to the strain gauges 2a and 2b can be outputted, and the cross-sectional stress is measured by using the output.