To automatically display the number of balls and their speed by sensing the movement the wrist in pitching and transmitting a signal with a transmitter in a wristband around the wrist of a pitcher, by sensing the impact of arrival of the ball and transmitting a signal with a transmitter in a mitt of a catcher, and calculating and displaying the ball speed by difference in the arrival times of the signals.

A transmitter 3 is installed in a wristband 2 around the wrist 1 of a pitcher, a transmitter 6 is installed in a mitt 5 of a catcher, and a receiver 4 is installed in the intermediate position between the pitcher and the catcher. When the transmitter 3 installed in the wristband 2 senses the movement of the wrist in pitching and transmits a signal to the receiver 4, and when the ball is arrived in the mitt 5 of the catcher, the transmitter 6 of the mitt 5 senses the impact and transmits a signal to the receiver 4. The receiver 4 calculates the time required from the arrival difference in the signals between the transmitter 3 and the transmitter 6 to display it on a display board 7. The receiver 4 can accumulate the data of the ball speeds of that day and print them out as necessary.