A string-striking device of a piano by which static loading applied to a front end of a key on the playing side can be readily adjusted. Each key (3) is provided with a long weight lever (21) disposed along the length direction of the key 3 at an upper part of the key (3) on the side opposite of the key to the playing side. The weight lever (21) is arranged such that one end thereof is fixed to a piano body so as to allow the weight lever (21) to freely swing up and down, and the other open end, which can be vertically displaced, is brought into contact with the upper surface of the key (3) and applies its own weight on the key (3). Thus, the static loading applied to the key (3) can be adjusted by replacing the weight lever (21) without disassembling the string-striking device and removing the key (3).