PURPOSE: To prevent the formation of a protrusion on the outer surface of a concrete secondary product by supplying concrete from a concrete input unit into a form via a plug inserting unit and a concrete receiving tube, and then pushing a plug by an elastic member via a plug sending cylinder.

CONSTITUTION: The end of a plug inserting unit 12a is connected to a concrete receiving tube 3, a concrete input unit 12b is connected to concrete pressure feeding means, and a plug 7 is inserted into a bearer body 14. Then, a shutter switching cylinder 16 is driven to shut OFF a shutter body 10a, the feeding means and a form 1. Subsequently, a plug sending cylinder 11 is driven to discharge the plug 7 to a predetermined position. The body 10a is operated, the communicating part is exposed to supply ready mixed concrete into the form 1. When a predetermined quantity is placed, the body 10a is again shut OFF, the plug 7 is pushed to press the concrete into the form 1. At this time, the end face of the member 7b becomes flush with the inside surface of the form 1.