A seat frame assembling unit includes: a setting device and a setting robot. The setting device is driven in a state where side frames, a connecting frame, a pan frame, a member frame and an upper frame are arranged. The setting robot installs the side frames side by side and subsequently installs the connecting frame, the pan frame, the member frame and the upper frame between the side frames. The setting device moves the side frames to positions in which the side frames are to be assembled with the connecting frame, the pan frame, the member frame and the upper frame.