A sewing thread of a sewn portion provided in an air chamber of an airbag is prevented from being cut during manufacturing, and damage to the airbag starting from an end of the sewn portion is suppressed. An orientation film formed on a nearest surface to the liquid crystal layer on substrate has an initial orientation direction. The weight of the complex multiplying section is calculated by a weight calculating section. An optically transparent superstrate is attached to the top side. In each of the three first switching states, one of the three phases of the direct-current motor is periodically switched over between a first and a second input voltage, whereas the two other phases are continuously connected to the first input voltage.