A back check for a piano is provided for locking a returning hammer in a pivotal movement without fail and for saving the manufacturing cost. The back check is used for locking the hammer in a pivotal movement for returning after it has struck a string to prevent the hammer from rebounding. A back check, disposed at a location at which the hammer is locked, extends in a vertical direction, and has an adhering surface which rises in a central portion thereof in the vertical direction. An under felt is adhered on the adhering surface of the back check body. A sheet-like cushion material, which is adhered to the back check body to cover the under felt, is formed with a locking surface in a predetermined curved shape conformal to the adhering surface for locking the hammer.