An information-acquiring device for acquiring information on an objective substance to be detected, which is provided with a sensing element that has a surface capable of fixing the objective substance to be detected thereon, and makes applied light change its wavelength characteristics in response to the fixed state of the objective substance to be detected onto the surface, a light source, and light-receiving means for receiving light emitted from the light source through the sensing element, has the light-receiving means and the light source arranged on the same substrate so that the light which has been emitted from the light source and has been transmitted through the sensing element can be led to the light-receiving means, and has means for varying the wavelength regions of each light incident on each of a plurality of the light-receiving means installed in an optical path from the light source to the light-receiving means.