A solid electrolyte body is placed on and fixed to an upper plate of a press jig such that a major surface (an upper surface) of the solid electrolyte body faces one major surface of a guide plate having an open space. The upper plate is rotated by a transfer mechanism to incline the solid electrolyte body in one direction, and the inclined solid electrolyte body is moved toward the other major surface of the guide plate such that a first edge of the solid electrolyte body protrudes from the open space. Then, a cutter is slid along the other major surface, so that the first edge is chamfered to form a first chamfered portion.