To realize the molding of a concrete secondary product having a smooth outside surface by a method wherein a means for guiding a charging ready-mixed concrete to the molding surface of a side plate on the upper side of the side plate of a form.

The ready-mixed concretes 2 charged through both outside charging ports 3b and 3b of a ready-mixed concrete charging machine 3 are guided from inside surfaces 8c and 8c through the inclined parts 8a and 8a of guiding means 8 and 8 to the forming surfaces 5a and 5a of side plates 5 and 5. At this time, the cement content in the mortar of the ready-mixed concrete 2 adheres along the forming surfaces 5a and 5a due to its viscosity, resulting in forming mortar layers 9. Similarly, the mortar layers 9 are formed on the inside surfaces 8c and 8c of the inclined parts 8a and 8a and at the upper end parts of the forming surfaces 5a and 5a. The ready- mixed concrete 2 passing through the center charging port 3b similarly forms a mortar layer 9a along the forming surface 7b and both forming surfaces 7a and 7a of an inner form 7. As a result, the outside surface of a concrete secondary product is made into a mortar layer, in which a small quantity of sand is included and which has a smooth surface.