PURPOSE: To increase the heat conductive coefficient and the evaporating quantity per a unit area by providing a liquid scatter preventing plate to an outlet of vapor from a heat conductive surface of a plate shaped liquid film flow-down type evaporating boiler in an inclined manner at a predetermined interval.

CONSTITUTION: To an outlet side of vapor from a heat conductive surface 5 of the plate shaped liquid film flow-down type evaporating boiler, a scatter preventing plate 6 is attached in an upwardly inclined manner at a predetermined interval. Thereby, the evaporated vapor "a" is discharged from a space between the preventing plate 6 and the liquid is reflected by said preventing plate 6 even if the liquid is about to escape therethrough with the evaporated vapor "a" and returned to a side of the heat conductive surface 5. This apparatus is effective as an evaporating boiler of a liquid which is deteriorated by high temp. heating and has high heat conductive coefficient. It is suited to a liquid evaporating boiler having increased quantity of evaporation per unit area.