Disclosed is a high-efficiency manufacturing installation in which seamless steel pipe rolling and finishing lines are matched in capacity with each other and are formed into a single continuous lines.The high-speed rolling line extends to a straightening machine via a cooling equipment for as-rolled pipes and a heat treating equipment for pipes to be heat-treated and is further connected to a single-line finishing line via a nondestructive inspection machine and a cutting machine. The finishing line comprises each plurality of different finishing machines arranged along a variable feed pitch transverse transfer line, the plural number being selected in correspondence to the capacity of the rolling line. The cooling equipment and the heat treating equipment are designed so that each of them requires the same transfer time and thus there is no danger of causing any blank in the feed pitch spacing during the change-over between the as-rolled pipes and the pipes to be heat-treated.