PURPOSE: To provide the titled device with the same function as that of plural lasers and to attain miniaturization, by separating a light from one semiconductor laser light source oscillated in several longitudinal modes into different points spatially in each longitudinal mode, and reading out information from the points different spatially.

CONSTITUTION: A laser light A from the semiconductor laser oscillated in the longitudinal multi-mode and the lateral single mode is made incident to a flat reflection type diffraction grating 3 at a collimate lens 2 as a parallel light B and diffracted, and the diffracted light in different diffraction angles is focused as spots E1WE3 on a focus D of an image forming lens 4. The optical path of the reflected light reflected on a medium placed on the focus D passes through the lens 4 by taking the spots E1WE3 as new light sources, is changed at a beam splitter 6 and the image is focused on an array detector 7 as spots F1WF3, allowing to read out the change in the optical property of the medium placed on the focus D.