We propose a force sensor based on gold nanoparticles, which enable optical detection of force by measurement of the scattering light spectrum. Gold nanoparticles were dispersed on an elastomer sheet. The scattering spectrum changes due to strain were observed to investigate applicability of the sensor to force measurement. The force deforms the elastomer sensor body, and increases the interparticle distance of gold nanoparticles on the sheet. The increase of the interparticle distance gives rise to the scattering characteristic changes. We fabricated a prototype sensor using PDMS sheet and 40 nm of diameter gold nanoparticles. It was demonstrated that 21% strain induced 60% increase of scattering intensity of gold nanoparticles.