To form an annular friction material by bringing a plurality of fan-shaped friction materials into close contact with each other by uniformizing pressure between mutual materials of the plurality of fan-shaped friction materials to a clutch piston.

The mutual materials of the fan-shaped friction materials 10-1 to 10-8 formed by being punched in a fan shape of constituting a part of an annular or substantially annular friction material 10 are arranged in a substantially annular shape according to an arranging metal mold 30 in a noncontact state. The fan-shaped friction materials 10-1 to 10-8 are moved to a diametrically contracted metal mold 50. Then, the fan-shaped friction materials 10-1 to 10-8 are moved in the central direction of an annular shape so that diameters of the an-shaped friction materials 10-1 to 10-8 become small, and the mutual materials of the fan-shaped friction materials 10-1 to 10-8 are formed in an annular shape or a substantially annular shape. An adhesive is applied to one or both of one surface of a plurality of fan-shaped friction materials 10-1 to 10-8 and an interface surface of the clutch piston 60, and the clutch piston 60 is pressed to the plurality of fan-shaped friction materials 10-1 to 10-8, and the opposed surface is adhered to the clutch piston 60.