An optical scanner that obtains precise and clear image information independent of a position for scanning an object. A plurality of light receiving parts are each composed of a photodiode, for detecting the image information of reflected light, and a detecting lens structured so that the beam diameter of the reflected light at the paired photodiode is larger than a beam diameter w.sub.0 expressed by:w.sub.0=1.22.times.2l.sub.2 .lambda./W, where.lambda.:Wavelength,W:Exit pupil diameter of imaging means,l.sub.2 :Image point position,and as the imaging means is an optical element, the principal plane of which is approximately equivalent to the top of the plane, signal variation in a state in which reflected light outside of the photodiodes is reduced.