Substrate (1) is used in light irradiation, is the multiple unit substrates (10) for having can cut off mutually with flexible base board (11) and coming. A part of unit substrate (10) has a pair of outer interconnecting piece (21). In the first face of flexible base board (11) in each unit substrate (10) setting LED chip (13) and wiring (12), back side wiring (19) are set across unit substrate (10) in the second face.