PURPOSE: To easily fit a sensor and to exactly discharge an emitted ball and a returned ball by arranging one sensor for playing ball detection along an emission rail and confirming either the emitted ball or returned ball when the pulse width of an output signal from the sensor is in a specified range.

CONSTITUTION: On the upper surface of an emission rail 140, a recessed groove is formed to guide the ball and on the front surface of a frame board 109, an emission sensor SNS 5 to detect the ball passing on the rail is mounted by a bracket 142. In the upper end of the fitting bracket 142, a returned ball block wall 143 is provided so that the returned ball can be prevented from jumping over the sensor. When the pulse width of the output signal from the sensor is in the range of 0.4-3.0mS, the ball is recognized as the emitted ball and when the pulse width is more than 3.0mS, the ball is recognized as the returned ball. Since one sensor is enough for detecting the emitted ball and returned ball, the sensor can be easily fitted. Then, a condition that the emitted ball collides with the returned ball and that erroneous detection is generated can be prevented and the noise of the sensor can be cut. Then, the exact number of held balls can be counted.