Method of manufacturing airbag cover, airbag cover, and airbag module

To provide a technique effective in rationally constructing an airbag cover for covering a vehicle airbag. An airbag cover 100 is machined with an ultrasonic machining blade 216. A tear line 102 in which a continuous groove with a depth within the plate thickness of the airbag cover 100 is formed such that the cross section becomes "a zigzag cut shape," "a sealer cut shape," or "a step cut shape," and the plan view becomes "a meandering cut shape."