A well casing cementing apparatus includes a housing and an inner assembly of movable parts. The housing includes a cementing port and a packer on its outer surface below the cementing port. The inner assembly includes three movable parts comprising a closing sleeve for closing the cementing port after a cementing operation, a closing sleeve seat for moving the closing sleeve and a packer setting sleeve for setting the packer. A rupture disk is provided closing the cementing port in a run in condition and is selected to have a rupture pressure at or above a pressure selected for setting the packer. An expandable collet on a lower end of the housing permits the closing sleeve and the setting sleeve to be pumped out the lower end of the housing, but prevents the pumped out parts from moving back into the housing, e.g. during production of fluids from the well.