Method for creating separation start portion for layered bodies, device for creating separation start portion, and electronic device manufacturing method

A method for creating a separation start portion for layered bodies in which, with respect to a layered body where a first substrate and a second substrate are attached so as to be separable with an adhering layer therebetween, a knife is inserted a predetermined amount from an end face of the layered body at an interface of the first substrate and the adhering layer and a separation start portion is created at the interface. The knife comprises a body portion, a cutting edge portion that is tapered in the side view and that is continuous with the body portion, and a ridge that is the boundary between the body portion and the cutting edge portion. At least a portion of the adhering layer is cut by a ridge portion that includes the ridge.