A surface acoustic wave filter is disclosed which comprises a piezoelectric substrate and at least two Interdigital Transducers having four fingered electrodes in a region corresponding to one-wavelength of SAW excited on the piezoelectric substrate. The mobile robot includes a video encoder, a bit rate analysis unit, an inference unit, and a switch unit. An inner catheter or elongate member having an occlusive device at its distal end is delivered to the site of the occlusion, and the occlusive device is activated at a site distal to the occlusion. The light projecting portion projects a light projection beam so that a converging position on the light receiving center axis is included within a range of the light shielding portion on the light receiving center axis for the component converged by the lens portion of the light projection beam specular reflected at the surface of the measuring target object.