Super-Kamiokande discovered the neutrino oscillation, hence it is confirmed that neutrinos have small but non-zero masses. However, their absolute values have not been determined yet.
On the other hand, we can also use cosmological observations to determine the mass of neutrino. In the universe, the matter distribution has density fluctuations and the growth of them is affected by relic neutrinos. Therefore we focus on the future precise observations of both the CMB polarization (e.g. POLARBEAR2 and Simons Array) and the 21 cm line (e.g. SKA: Square kilometer Array), and study their sensitivities to the sum of the neutrino masses. In this talk, I will talk about the results of our analysis and show that combinations of CMB polarization experiments and SKA can strongly improve errors of the bounds on the sum of the neutrino masses.