An information acquiring device has a light source which emits light of a predetermined wavelength band; a projection optical system which projects the light emitted from the light source toward the target area with a predetermined dot pattern; and a light receiving element which receives reflected light reflected on the target area for outputting a signal. In this arrangement, the projection optical system projects the light toward the target area in such a manner that a dot of a reference pattern of the light to be received by the light receiving element has a pitch equal to or larger than 2.5 pixels at least in an alignment direction in which the light source and the light receiving element are aligned.