PURPOSE: To provide a nozzle flapper mechanism for an electric-pneumatic converter which adjusts clearance between a nozzle and flapper according to fluctuation of a primary pressure side.

CONSTITUTION: A pressure chamber 6 is arranged adjacently to a back pressure chamber 1, to which primary side pressure and atomspheric pressure are introduced. The pressure chamber 6 is divided to a primary pressure introduction chamber 6a to which the primary side pressure is introduced and an atomspheric pressure introduction chamber 6b to which atmospheric pressure is introduced, by means of a diaphragm 8. An intermediate portion of a nozzle 12 is fixed to the diaphragm 8. A lower end of the nozzle 12 is inserted into a first through- hole 9 in a slidable manner, while an upper end thereof is inserted into a second through-hole 11 in a slidable manner. The primary side pressure is introduced into the back pressure chamber l and the primary pressure introduction chamber 6a, respectively through a first branched passage 4a and a second branched passage 4b. When the primary side pressure is fluctuated, the diaphragm 8 and the nozzle 12 are also moved vertically. A clearance between a nozzle and a flapper is adjusted for eliminating unstable factor of a system.