The present method of forming a groove in an inner surface of a member for covering an airbag includes the steps of heating a blade by use of an induction-heating device and pushing the blade against the inner surface of the member. The induction-heating device is preferably a coil for induction heating. In addition, the present method of forming the groove preferably includes the steps of placing the member on a work bench having the coil, supplying alternating current to the coil, bringing the blade close to the coil, pushing the blade against the inner surface of the member, stopping current supply to the coil, and pulling the blade away from the inner surface of the member.