PURPOSE: To provide a small-sized ball sensor used in a pachinko game machine which can precisely detect a game ball without being influenced by electromagnetic waves.

CONSTITUTION: A ball sensor 10 used in a pachinko game machine has a ball passage part by a through hole 15 and a switch housing part 21. This ball sensor 10 has a detection lever 14 partially protruded to the through hole 15 through the front wall 22 of the switch housing part. The switch housing part 21 contains a photoelectric switch having a light emitting part and a light receiving part arranged with the detection lever 14 between in the rear of the detection lever 14, and the detection lever 14 detects a game ball 71 by the photoelectric switch which is turned on or off by the detection lever 14 recessed into the switch housing part 21 by the game ball passing the through hole 15.