A hybrid keyboard musical instrument is fabricated on a piano, and a hammer stopper and an electronic tone generating system are installed in the piano; the electronic tone generating system includes hammer sensors arranged on a framework secured to a shank flange rail by means of stud bolts, and the stud bolts and spacer nuts, which are threaded with the stud bolts, serve as locators for locating the sensors at target relative positions with respect to the hammers independently in the fore-and-aft direction and up-and-down direction; the framework is pressed to the spacer nuts with nuts driven into the stud bolts so that the framework is removable from and reassembled with the shank flange rail without loosening the stud bolts.