An optical modulator in which stabilized driving is realized over a long time by relaxing stress generated in a recess formed in the surface of a substrate in the optical modulator and controlling deterioration of optical modulation control caused by stress-strain in the substrate including an optical waveguide. A mobile station, such as a cellular telephone for instance, may be registered with an instant messaging server as being available to receive instant messages via an IM proxy. The conveyor belt has supporting beams disposed at a distance apart and at the ends of which are rollers, which roll along the middle and lower supporting cables.