In a clutch manufacturing method, inner peripheral portions of drum members, of two clutches are connected to a sleeve member, and a piston, a seal plate and a return spring are provided between the drum members, an insulator to apply electric isolation between the piston and the drum member or between the seal plate and another drum member is attached to either the piston or the seal plate. Then, the drum member, to which the electric isolation with the insulator is not applied, is connected to the sleeve member. Then, the piston, return sprig and seal plate are assembled to the sleeve member to which the drum member has been connected. Finally, the drum member, to which the electric isolation with the insulator has been applied, is connected to the sleeve member with electric welding.