Abstract: The present invention intends to provide a musical instrument that is improved in the acoustic performance, expanded in the capability of sound expressions in musical performance and suitable for kinds of string instruments more than existing solid guitars, solid base guitars and other string instruments. In a string instrument that generates musical sounds based on a vibration of a string stretched over a resonant body, the resonant body is formed on a basis of three-layer structure made of a top plate, a back plate and an intermediate plate interposed between the top plate and back plate, the top plate and back plate each being made of a single panel that is cut so that a woodgrain direction is a plate surface direction, the intermediate plate that is cut so as to come into contact with the top plate and back plate at end grain being laminated with the top plate and back plate at the end grain, and thereby a resonant body structure is constituted.