A revolving-frame structure of a hydraulic shovel installed on a revolving body (21) and having a center frame (1) in which side plates (6) and (7) are connected to each other through a partition wall (8), comprising an engagement part for engaging the side plates (6) and (7) to the partition wall (8). The engagement part further comprises an insert structure part having holes (6a) and (7a) formed in the side plates (6) and (7) and projected parts (8a) and (8b) installed at both side edge parts of the partition wall (8) and inserted into the holes (6a) and (7a) in the side plates (6) and (7).Thus, the center frame can be manufactured without requiring holding jigs for fixedly holding the side plates to a bottom plate.