A novel measurement method for evaluating hydrogen solubility in water is developed Purified water is exposed to high-pressure hydrogen in a gas-liquid equilibrium cell of approximately 100 cc, and than gaseous component in the water sample of approximately 10 cc is analyzed with quadruple mass spectrometry. The purpose of this study is to establish hydrogen solubility data in water up to 29 MPa and to 75 ℃. Preliminary measurements under low pressure (up to 1 MPa) show that the deviation of measured solubility lies within the range of the estimated uncertainty of measurement. We reveal that the measurement uncertainty of the present method highly depends on the background intensity for hydrogen in the mass spectrometry.