An apparatus for roll-forming a blank ring into an annular product such as a seamless wheel rim. The apparatus includes an annular die rotatably supported in a die head, and a pressure roll rotatably supported in a roll head and movable toward and away from the annular die. The apparatus further includes a cylinder unit for moving the pressure roll radially of the annular die when the pressure roll is in the annular die, whereby the blank ring can be interposed between the pressure roll and the annular die. As the die is rotated, the blank ring is roll-formed between the roll and the die into an annular ring, which then is confined in the annular die and can be taken out when the die is disassembled into a plurality of segments. The product thus formed has a high degree of circularity and precision, and is free from distortions.