PURPOSE: To prevent an object from colliding with a casing by reducing the outer shape size of the casing.

CONSTITUTION: A light source 2 arranged in a casing 1, a mirror 6 located to the outer frame of the casing 1, and a means to regulate an effective illumination region 5 are provided. The outside is irradiated with illuminating light from the light source 2 once and the illuminating light is reflected by the mirror 6. By producing an illuminating state similar to a state that the light source is located outside the mirror 6, the outer shape size of the casing 1 is reduced. The effective illuminating region 5 is regulated by the regulating means, and a clearance between the casing body 1 and an object is kept and the casing is prevented from colliding with the object.