Beyond the local universe, neutral hydrogen (HI) gas, a tentative star formation reservoir, is poorly constrained by observation, compared to star formation. It is because existing observing facilities in radio frequency to detect HI 21-cm emission lines are not sensitive to directly measure weak HI signals from individual galaxies at z > 0.2. To overcome the sensitivity limitation, two new techniques have been proposed and recently proved their viability. One is HI spectral stacking technique, and the other is HI intensity mapping. These are the most promising techniques to push the sensitivity limit of even future radio facilities such as SKA pathfinders and SKA still further. In this talk, I will present how HI gas content of galaxies in the intermediate redshift 0.1 < z < 0.4 has been measured using the HI spectral stacking that I used in my previous works and briefly introduce an HI intensity mapping experiment which I am heavily working on at the moment.