An assembling device (10) includes a first arranging section (11), a second arranging section (12), eighteen support arms (13) for supporting coil segments (4), a feeding part (14), and a controller (16). When the controller (16) drives a motor (35) to rotate the feeding part (14) in a counterclockwise direction D1, a pressing roller (14c) rolls in the direction D1 along a first guide portion (11a), and presses a base part (21) of the eighteenth support arm (13) in the direction D1. Thus, the first to eighteenth support arms (13) are rotated in the direction D1 to insert the base parts (21) of the first to eighteenth support arms (13) sequentially in a second guide portion (12a) of the second arranging section (12), so that the first to eighteenth support arms (13) are rotated in a clockwise direction D2 to assemble the coil segments (4) while overlapping with one another.