A truer includes: a core formed into a truncated cone; and an abrasive grain layer fixed onto an outer peripheral surface of the core. The core includes: a base that is a small-diameter portion of the truncated cone and has a disc shape; and a tubular member extending from an outer peripheral edge of the base in the direction in which a rotation axis of the truncated cone extends. The tubular member has a hollow tubular shape. The tubular member includes an outer peripheral surface tapered so that a portion of the tubular member opposite to the base and adjacent to an extremity of the tubular member is a large-diameter portion of the truncated cone. A recess opening toward the extremity is defined inward of the tubular member.
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