Abstract: A device (1) for measuring the strike velocity of a game ball struck by a striking element, particularly a tennis racket (2), said device being provided directly on the racket. The device comprises at least one measuring sensor mounted on the strings (4) of the racket (2) and arranged to output signals for the strength of the vibrations generated by the ball, means for processing said signals using microprocessors that analyse the signals and determine a measured value of the ball velocity, and means (6) for displaying said value. The processing means comprise a calibrating unit for automatically correcting the measured value depending on at least the features of the racket and the ball in order to provide a highly accurate and reliable result. Said measuring device is miniaturised and inexpensive and fits in a small housing (3) mounted on the racket (2) to enable the player to read the velocity value directly.