A flat light source apparatus has a light source board which comprises unit boards, each unit board having a printed circuit board and a light source formed on the printed circuit board, wherein the unit boards are arranged adjacent to each other at least in one direction, and any pair of the unit boards adjacent to each other is integrated by a connecting portion provided therebetween. The apparatus also has a main wire which extends along a plane of the light source board, wherein the main wire extends between adjacent unit boards via the connecting portion such that all of the unit boards are electrically connected to each other by the main wire. The apparatus further has a branch wire for supplying electric power to the light source, the branch wire being provided in each unit board and branching from the main wire in each unit board.