A jack and push/pull apparatus is provided by attaching to a wellhead an extendable/contractible horseshoe-shaped jack assembly of sufficient diameter to surround and act upon the tubing or casing to be manipulated in the well, the linear action of the assembly being powered between an extended and a retracted position, the assembly having at least one tube-gripping mechanism at the end of the assembly away from the wellhead attachment. Tubing is inserted into the well bore through the assembly and the wellhead, and when injection forces are desired tube-gripping means grip the tubing being injected and the apparatus is powered to a retracted position, forcing the grasped tubing into the well. The operation may be reversed to pull tubing or casing. The assembly can be simply added to the rig while tubing is present on and above the rig's floor.