PURPOSE: To simplify slide control and to permit the easy change and addition of control language by instructing and changing over whether the voice input signal from a sound input part is for explanation of a slide or for control by an instructing means and recognizing the voice input signal when the instructing means is for the control.

CONSTITUTION: Voice is inputted from a microphone 21 of a voice input part 2 and when the input voice from the operator is for the explanation of the slide, a selector switch 22 is held as it is. The switch 22 is operated to transmit the signal from a transmission part 23 to a reception part 11 of a projector body 1. The sound signal is recognized in a recognizing part 12 which operates a slide control part 13. The voice is outputted by a speaker, etc., to the outside to permit the easy operation of the slide control if the input voice is for the explanation of the slide.