A fixing device of a solar cell unit, comprising a long mounting frame (10) secured to a roof, module securing metal members (30), and a frame member (3) having a part (3e) to be clamped by the frame (10) and by the module securing metal members (30) and having a groove part (3c) for supporting an end part of a planar solar cell unit (2). The frame member (3) is formed such that the part (3e) to be clamped is located inside a region where the solar cell unit (2) and the groove part (3c) are projected directly downward, thus reducing the distance between adjacent solar cell units (2).
