It is an object of the present invention to provide an optical component provided with a demultiplexing function capable of reducing an insertion loss and downsizing, and a wavelength dispersion compensator using such an optical component. In order to achieve the object, according to the optical component provided with the demultiplexing function of the present invention, in a configuration of VIPA type in which an incident light is multiple-reflected between two reflective surfaces that are opposed and parallel to each other, and due to the mutual interference of the multiple-reflected light, optical beams, traveling direction of which are different from each other according to wavelengths, are formed, an incident light is given from a first side surface substantially perpendicular to the reflective surfaces, and is reflected by a second side surface opposed to the first side surface, to be sent to either of the parallel reflective surfaces, thereby causing the multiple-reflection between the reflective surfaces.