An optical tweezers device determines trapping force data indicating a trapping force for a particle on the basis of a distance between the particle trapped by focusing laser beam with a lens and a focal point of the lens. The optical tweezers device determines a difference between a trapping force theoretical value that is estimated according to a linear relationship between the distance between the trapped particle and the focal point of the lens and the trapping force for the particle and the trapping force indicated by the trapping force data. The optical tweezers device controls a laser power of the light source on the basis of the difference of the trapping force.