Japan Aerospace Exploration Agency (JAXA) is currently developing the pre-cooled turbo jet engine (PCTJ) for hypersonic flight. This engine features air pre-cooling using liquid hydrogen fuel in advance of the compression. The cryogenic hydrogen fuel changes drastically in density when it evaporates while passing the fuel tubing at the engine start-up. Presently, the inadequacy of the physical property data of two-phase hydrogen flow pertaining to evaporation hinders the construction of the fuel flow simulator required in establishing high accuracy fuel flow control. In the present study, a device for the void fraction measurement is developed, that is a key parameter of the characteristics of the two-phase flow. It uses the difference of the electric permittivity between the liquid and gas. Validation tests comparing with the optical method were conducted by oil/air, nitrogen and hydrogen. The electrical heater produces various evaporation modes such as bubbly flow, slug flow and churn flow. The void fraction meter could successfully acquire the physical property even in a cryogenic condition. We also measured the heat transfer coefficient of the cryogenic two phase flow. The data of the nitrogen flow arranged by well-known Lockhart-Martinelli parameter shows the agreement with the analytical value.