A method of manufacturing individual strain sensors (20) each comprised of a generally rectangular substrate (21) having first and second major surfaces opposite to each other, a strain detecting element (23) formed on the first major surface of the substrate and having at least one pair of strain sensing areas (23a), and a pair of grooves (24) defining respective areas (21a) of low rigidity and formed in the second major surface of the substrate (21) at respective locations adjacent the opposite ends of the substrate (21) while extending across the width of the substrate with the strain sensing areas (23a) of the strain detecting element (23) positioned in register with the respective grooves (24). The strain sensors (20) are prepared from a single plate material (30) of any suitable size having first and second surfaces opposite to each other and eventually forming respective substrates (21) of the individual strain sensors (20). A plurality of spaced groove segments (31) are formed on the second surface of the plate material (30) so as to extend parallel to each other, and a plurality of strain detecting elements (23) are subsequently formed on the first surface of the plate material (30) in a substantially matrix pattern so as to assume a predetermined positional relationship with respective positions of the groove segments (31). Thereafter, the plate material (30) is cut along cutting lines (b) extending in two different directions to separate the individual strain sensors (20).