A hammer strike line adjuster for use with a grand piano comprises a metallic, generally U-shaped bracket, a worm gear rotatably received within a pair of aligned apertures formed in the side walls of the bracket and a shift pin having a first end secured to the piano key frame assembly and a second end engaging an annular recessed portion of the worm gear for movement together therewith. The apparatus, which is disposed between the piano key frame assembly and treble arm and underlying the piano key block, is operative for accurately adjusting the position of the piano hammer strike line in response to rotation of the worm gear.