Super-Kamiokande (SK) experiment started the "SK-Gd experiment" by dissolving gadolinium (Gd) sulfate octa-hydrate in ultra-pure water from the tank in July 2020. The neutron tagging efficiency has been improved compared to the pure-water phase by detecting a total energy of $8 \rm{MeV}$ gamma rays emitted by thermal neutron capture on Gd. It enables us to improve, for example, the sensitivity of diffuse supernova neutrino background, the accuracy of the reconstruction for the supernova direction, and so on. For these physics targets, accurate evaluation of neutron identification efficiency is essential. In this presentation, I report the calibration results using an Am/Be neutron source to evaluate the efficiency at a Gd mass concentration of 0.03\%, starting from June 2022, and the comparison of the estimated neutron detection efficiency with simulation.