To improve the yield of the rubber material, and to prevent the early deterioration of a board of a gasket due to the high temperature and high pressure by forming a gasket without applying high temperature and high pressure as a rubber vulcanizing condition.

This method of forming a gasket 1 having the predetermined cross section, to which a rope-like rubber seal part 7 is adhered, includes a process for forming a rubber ground 7' to be formed into a rubber seal part 7 into a rope shape, a process for forming the rope-shaped rubber ground 7' into the predetermined cross section, a process for vulcanizing the rubber ground 7' having the predetermined cross section so as to form a rubber seal part 7, and a process for adhering the rubber seal part 7 to the board.