To provide the detector and the management device for plying balls, which have a faster detection response speed with less detection errors and are hardly restricted of the mount space.

The device is provided with a coil 1, placed at a prescribed position in the vicinity of a path of a playing ball 8 made of a magnetic material, a circuit 3 that excites the coil 1, a circuit that generates a signal representing it that each playing ball passes in the vicinity of the coil 1, based on the measurement of a phase lag of an output signal produced proximity of the ball 8 with respect to the coil l, and also with a means that counts number of playing balls passing the proximity of the coil 1. Or the passing direction of the playing ball is detected in the order of proximity of balls to two coils.