In a method and device performing a change of a line type without saving a service line to a protection line in service at a line level when a unit in service is updated in a transmission device or the like composing a SONET network supporting various types of line connections, when it is analyzed that a control command is requesting a type change of an active line, a change request line in addition to the active line is redundantly managed, and a redundant setting of a line is performed based on line connection setting information of the change request line, and a switchover of the active line to the change request line is performed depending on whether connection destinations of both lines are different or same.