A light diffusion box for photographic use comprises a box body which has an inner surface for reflecting light and an opening at its one end, a light source mounted at the bottom of the box body, and a light-transmitting member. The light-transmitting member includes a light-transmitting area having a specific shape and a light-blocking area formed at the periphery of the light-transmitting area. The light-transmitting area may is of any suitable shape, such as any one of circular, elliptic, stripe, quinquangular, octagonal shape. By forming a light-transmitting area having a specific shape in the light-transmitting member, the light spot projected from the soft light box can exhibit any specific shape, thereby meeting the need of a variety of purposes in photography.