To provide a manufacturing method of a grooved plug capable of easily manufacturing a grooved plug by cold heading, shaping a circumferential groove part without lowering in strength, causing no projection of a protruded burr in shaping, and also extending the life of a die.

At first, in a cold heading step S4 for a front side, the diameter of one end of a cylindrical stock b is reduced by cold heading to form an intermediate product 1C having a polygonal head part 3' with a larger diameter than other parts. Next, in the cold step S4 for a rear side, while holding the head part 3' of the intermediate product 1C is held by a punch 33 and an upper part 25a of a shaping hole of the die 25, the shaft part 2' of the intermediate product 1C is pressed into the depth part of the shaping hole of the die 25, and the shaft part 2' is cold-headed by the die 25 having a lower part 25b of the shaping hole with a larger diameter than the shaft part 2' and projecting a center pin 28 at the center of the depth part of the shaping hole to increase the diameter on the tip end side of the shaft part 2', thereby shaping the circumferential groove part 4 on the boundary of the head part 3 and the shaft part 2 to manufacture the grooved plug.