Abstract: Portable apparatus for automatically constructing prefabricated stud walls or other frame structures from standard materials. Elongate studs are placed transversely at spaced intervals between a pair of elongate wall plate members by a reciprocatingly rotating stud-selecting mechanism and a linearly reciprocating spacer mechanism. As each stud is placed between the plate members, it is automatically nailed thereto, forming a portion of the wall frame, after which the completed portion of the frame is advanced an incremental distance along an assembly structure by the spacer mechanism, which pushes on the newly nailed stud to advance the frame to a position for nailing the next succeeding stud, and so forth in automatic cyclic fashion. A semi-automatic sheathing fastener mechanism includes a plurality of fastener guns and an automatically controlled actuation mechanism for placing fasteners at predetermined locations.