To prevent the attention of the audience from being distracted due to an expositor being away from the position of a screen for conducting operatations at a computer in the presentation to be performed by magnifying and projecting the screen of a personal computer by a projector.

The video signal of a computer 3 is magnified and projected on a screen 5 by a projector 4 to conducting a presentation. An expositor 6 performs explanation while pointing the surface of the screen 5 with a pointing device 1 and by touching the surface of the screen 5 with the top end of the pointing device 1 or pressing a switch provided on a grip part, an ultrasonic wave modulated by a correspondent code is transmitted from the pointing device 1, received by a reception part 2 and transmitted to a computer 4, so that page feeding or predetermined operation can be performed.