To certainly prevent the malfunction of an operation member in a direction to open a mobile piece in a closing posture.

An operation member 3 which is supported by pivoting at an approximate middle section to incline and is installed in a case 2 puts the mobile pieces 4A and 4B in the closing postures when its front end section 34 is moved downward by the load of the contact of a first prize-winning ball which enters while the mobile pieces 4A and 4B are in the opening postures with the side of the front end section 34, and puts the mobile pieces 4A and 4B in the opening postures when the front end section 34 is moved upward by the load of the contact of a second prize-winning ball which enters the rear end section 39 side of the operation member 3 while the mobile pieces 4A and 4B are in the closing postures with the rear end section 39 side. A rise controlling member 6 moves to a controlling position to control the rising motion of the front end section 34 of the operation member 3 in a lowering situation and is moved to the outside of the controlling position by the entering of the second prize-winning ball.