An assembling device (10) includes a first rotating portion (11), a second rotating portion (12), and eighteen support arms (13) for supporting coil segments (4), and a motor (29). The first rotating portion (11) includes a first rotating plate (11a) having first holding portions (1d) on an outer peripheral surface thereof. The second rotating portion (12) includes a second rotating plate (12a) having second holding portions (12c) on an outer peripheral surface thereof. The motor (29) rotates the first rotating portion (11) in a counterclockwise direction D1, and the second rotating portion in a clockwise direction D2. Thus, the base parts (21) of the first to eighteenth support arms (13) are transferred from the first holding portions (11d) to the second holding portions (12c) so that the coil segments (4) are assembled to overlap with one another.