Apparatus for assembling curved skin block frames of a hull, which comprises (1) sets of oppositely disposed devices for positioning slotted transverse reinforcing members which have a transverse member clamping mechanism for holding the transverse members near both ends thereof in such a manner that the slots of the transverse members face downwardly and so as to position several transverse members therebetween, a transverse member supporting stool, a mechanism for adjusting the oblique angles of the transverse members, and a mechanism for adjusting the positions of the elevational direction, longitudinal direction and transverse direction of the transverse members; and (2) a device for positioning longitudinal reinforcing members, which comprises a longitudinal member clamping device for carrying longitudinal members corresponding to the slots of the transverse members, positioned previously in tentative longitudinal member positions, so as to insert the longitudinal members from the underside of the transverse members into the slots thereof, a longitudinal member supporting stool, a mechanism for adjusting the oblique angle of the transverse direction of the longitudinal members, a mechanism for adjusting the oblique angle of the longitudinal direction of the longitudinal members, a mechanism for adjusting the position of the longitudinal direction by lifting the longitudinal members, and an assembly for carrying the longitudinal members from the tentative longitudinal member positions to the slot positions; and a method therefor.