PURPOSE: To obtain flash vapor of high degree of dryness by providing a water resistant injection nozzle, a flash chamber, a sepn. chamber, and a flow regulating plate which is erected near the vapor outlet and has many through-holes in a body cylinder of a flasher.

CONSTITUTION: The geothermal water ejecting through an injection nozzle 13 turns to flash vapor and further it is thoroughly separated of vapor and unflashing drains by the effect of a body end plate 20 and a drain separator 14, after which the flash vapor contg. a trace amt. of scattered water drops flows through a vertical perforated plate 17 into a sepn. chamber 21. In the chamber 21, the vapor flows uniformly in a horizontal direction at a low velocity of flow and in this section, the water drops falls by the effect of gravity. Before the vapor reaches a flow regulating plate 19, the vapor hardly contains water drops and in this state it passes through through-holes 26, turns upward toward a vapor outlet 15. The vapor is fed to a steam turbine 3 through a vapor outlet 15.