| 摘要 |
A surface 60 of a butt 50 has a flat portion 61 which is situated forward and has a small inclination angle and a slanting pressure receiving portion 62 which is situated backward and has a large inclination angle as areas pushed up by a jack 40. Between the flat portion 61 and the slanting pressure receiving portion 62, an escapement portion 63 having an obtuse angle is formed. The escapement portion 63 is provided to correspond to a position of the jack 40 placed immediately after the start of swinging of the jack 40. The inclination angle of the slanting pressure receiving portion 62 is determined such that in a stage where a key starts returning from a slow full stroke key-depression, a position at which the butt 50 is in contact with the jack 40 is maintained with the butt 50 swinging backward.
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