An electrical device configured to be provided in a vehicle includes a first case; and a second case that is fastened to the first case by a bolt. A side surface of the first case is provided with a columnar projection that extends along the side surface. The columnar projection is provided with a bolt insertion hole through which the bolt is inserted, the bolt insertion hole extending along the side surface. A center line of the bolt insertion hole is located closer to a center of the first case than a center line of the columnar projection is.