A new photothermal technique for sensing the tension in a small mechanical beam is described. The irradiation of chopped laser light on the beam produces a flexural resonance vibration whose amplitude is of the order of a nanometer. An axial tensile force changes the resonance frequency of the vibration slightly. By optically monitoring the frequency change, the tensile force acting on the beam is detected from a distance. Preliminary results suggest that the proposed technique will be useful for sensing tension in inaccessible environments and for development of new optical sensors associated with force and pressure.