The structural change of formate on NiO(111) by irradiation of intense picosecond laser pulses of 1064 nm wavelength was studied by sum frequency generation (SFG) spectroscopy. The peak due to the bidentate formate (DCOO) was observed at 2160 cm^-1 without the irradiation. When the laser pulses was introduced to the surface, the peak at 2160 cm^-1 decreased in intensity and new peak appeared at 2190 cm^-1. The newly observed peak was assigned to monodentate formate. The bidentate formate was found to be transformed to the monodentate formate by the transient temperature jump induced by the irradiation and the monodentate formate was regarded as an intermediate of thermal decomposition of formate.