a valve - position output apparatus capable of adequately detecting valve - positions on an optical basis . the valve - position output apparatus for a valve comprises an interlocking member arranged to move in sync with open and close operations of the valve , a position detecting aperture formed in said interlocking member , an optical encoder having a light - emitting section and a light - receiving section which are arranged opposed to each other with interposing the interlocking member therebetween , digital valve - position signal generating means for generating a digital valve - position signal on the basis of a signal from the optical encoder , and initial setting means for initializing the digital valve - position signal generating means so as to match the digital valve - position signal of the digital valve - position signal generating means with an actual valve position .