A weight for a key of a keyboard musical instrument that is to be inserted and secured in an attachment space, provided to the key, is provided. The weight includes: a weight body portion; and a corrugated portion, disposed in at least one portion of a lateral surface of the weight body portion, the lateral surface being located around an axis extending in an inserting direction of the weight body portion into the attachment space, the corrugated portion including a plurality of corrugations aligned in the inserting direction. The weight body portion and the corrugated portion are made of an elastic material.