To enable a silencer to be attached to an existing keyboard instrument, using a simple constitution.

A hammer shank stop rail is supported by a plurality of poles and a plurality of link mechanisms through the use of the center rail of musical instrument body and is made to advance into an operation range of a hammer shank against an energizing force of an energizing means. Also, the mounting position of the hammer shank stop rail can be easily changed, according to the height of the hammer shank of an existing keyboard instrument, and the mounting positions of the link mechanisms and the hammer shank stop rail can be changed so as not to cause interferences, according to the positions of the string and section of the existing keyboard instrument.