A device comprises an engine including a crank shaft with a first end portion, a generator motor including a rotor shaft with a second end portion, a flywheel with first and second connection portions connected to the first and second end portions respectively, and a fastening member. At least one of the connection portions constitutes an alignment connection portion. The first or second end portion constitutes an alignment end portion. One of the alignment connection portion and the alignment end portion includes a concave portion having an alignment inner surface, and the other includes a convex portion having an alignment outer surface. One surface of the alignment inner and outer surfaces is a tapered surface. The fastening member fastens the alignment connection portion and the alignment end portion to each other to bring a tip end of the other surface into pressure contact with the tapered surface.