To provide a coordinate inputting device capable of efficiently facilitating a countermeasure even to a large-scaled whiteboard, and operating not only the writing of data in the whiteboard face but also the erasure of the written data.

This coordinate inputting device for irradiating the plane face of a whiteboard 11 with lights, and for inputting position coordinates on the plane face based on the reflected lights of the lights is composed of an instructor 13 having a site 10 formed of a reflecting member for reflecting lights to an incident direction, an optical unit 14 having a light source part for irradiating the plane face with lights and a light receiving part for receiving the reflected lights from the instructor 13, and a processing part 15 for calculating the position coordinates of the instructor 13 on the plane face based on the reflected lights received by the light receiving part of the optical unit 14.