A piecing apparatus for a doubler provided with a processing robot which moves along units of a doubler. The piecing apparatus comprises two piecing devices, a suction mouth for sucking and holding a yarn on the side of a winding package to guide it toward the piecing device, a relay pipe for sucking and holding a yarn on the side of a feed package to guide it toward the piecing device, an upper yarn separating device for separating a doubled yarn on the side of each winding package guided toward the piecing device, and a lower yarn separating device for separating a yarn on the side of each feed package guide toward the piecing device.