To ensure the accuracy in a curved surface and the finish of a concrete texture in a favorable condition without using a formwork, by curving and placing a rock-wool lath while providing a gradient corresponding to the curved surface and blasting concrete.

A meshed rock-wool lath 1 which can change itself from a folded state to a spread state where the mesh spreading like a honeycomb continuously is prepared. The rock-wool lath 1 is bent while giving a gradient corresponding to the curved surface of a concrete to be molded and securing a prescribed thickness and is placed. In this case, not formwork is used. The curved shape of the rock wool lath 1 is retained in a desired form by using a guide 3 along the gradient of the curved surface and a reinforcement 4 intersecting it. After concrete 6 is blasted to the rock-wool lath 1 from a blasting nozzle 5, surface finishing is made.