PURPOSE: To produce a cap nut of a good finished state easily by bringing rollers which revolve at a high speed into contact with the hollow cylindrical body of the head part of a nut body thereby forming a sealed state cap.

CONSTITUTION: After a nut body 2 formed with a hollow cylindrical body 1 corresponding to a cap part into one body is tapped, the body 2 is fixed to a die 3 and is revolved at a high speed. Plural pieces of rollers 4 which move forward, backward, right and left while revolving at a high speed like the die 3 in the direction opposite from the die 3 are brought into contact with said body 1 from its outer side. The body 1 softens by the friction heat of the rollers 4, and is formed to a prescribed cap shape by the rollers 4. Further, the end parts are heated to high temp. and are melt stuck to form a sealed state cap. Next, the burrs produced by the overlapping of the upper end parts of the body 1 are cut off, and the product is obtained.