A musical tone control system for a grand-type piano, which not only enables a shutter to be mounted on a hammer without any inconvenience even when a space above the hammer is small, but also is capable of properly controlling musical tones to be sounded. In this system, first to third optical sensors are disposed along the length of a hammer shank. Depression or non-depress of a key and a pivoting direction of an associated hammer are determined based on signals from the first and second optical sensors, respectively. Further, the pivoting speed of the hammer is calculated based on a signal from the third optical sensor. A musical tone to be sounded is controlled based on the determined depression or non-depression of the key and pivoting direction and the calculated speed of the hammer.