Abstract: A fastening device includes first to third rotary sensors (position detecting unit) which are provided in a support arm and detect a position of a nut runner (fastening tool), and a main controller (controlling unit) which has a storage unit for storing a plurality of fastening positions of a chain cover, and drives the nut runner when a detection result from the first to third rotary sensors coincides with position information of the fastening position of the chain cover stored by the storage unit. Therefore, during a fastening work, an operator does not need to pull a trigger to drive and rotate the nut runner, thus reducing a burden on the operator during the fastening work.