Fastening device and fastening method of solar cell module

A fastening device which reduces the work by screwing and shortens the installation time has been desired. A fastening device 100 which fastens and supports a plurality of solar cell modules 20 includes a base part 111, a first module support part 113 which has a first support surface 113a and which is provided at the base part to be able to elastically displace, a second module support part 114 which has a second support surface 114a and which is provided at the base part, wherein the second support surface is arranged so that the second support surface is away from the first support surface of the first module support part when not elastically displaced at a constant first interval T2, a third module support part 123 which has a third support surface 123a and which is provided at the base part to be able to elastically displace, and a fourth module support part 124 which has a fourth support surface 124a, which fourth module support part is arranged a constant second interval T3 which is smaller than the first interval T2.