A second optical component is an optical fiber bundle charged in a clearance between an inner cylinder and an outer cylindrical outer peripheral part in the form of a ring. These elements are integrated with each other, and forward-end-surfaces thereof are on concentric circles. A ring of the forward-end-surface of the outer peripheral part is larger in width than the ring of the forward-end-surface of the second optical component. A first optical component charged with an optical fiber bundle is slidably inserted into and engaged in the cylinder inside the second optical component, so that the forward-end-surface of the first optical component can project or retract from the forward-end-surface of the outer peripheral part. The outer peripheral part is brought into contact with a human body and force for pressing a measured region is changed by sliding the first optical component for measuring absorption spectra between the first and second optical components under different values of pressing force, thereby obtaining a difference absorbance spectrum under different states of pressurization.