According to the present invention there is provided a space coordinates detecting device wherein a detecting section for detecting light emitted from a light source is provided, thereby permitting detection of a relative angle between a light emitting sections and the detecting section and hence permitting application of the detecting device to an input apparatus. The detecting section is provided with a light sensing element 23 having quartered light sensing portions. In the light emitting section, distinguishable lights are emitted from two light sources. The lights thus emitted are throttled through apertures and applied as separate square light spots S16 and S17 to the light-sensitive surface of the light sensing element 23. By calculating a difference in the detected output among the quartered light sensing portions, it is possible to determine the center I1 of the square light spot S16 and the center I2 of the square light spot S17. A relative rotational angle of the light emitting section and the detecting section with respect to Z axis can be determined by calculating an inclination angle .alpha. on X-Y orthogonal coordinates of a line x connecting both centers I1 and I2.