Provided is a feed opening adjustment device capable of finely adjusting the size in the height direction of the feed opening of a cage for raising chicks. The feed opening adjustment device (1) changes the size in the height direction of a feed opening which is a space that is open in the lower part thereof by raising and lowering a shield plate. The feed opening adjustment device is equipped with: an operating arm (10) for applying a raising or lowering force on the shield plate by being rotated in unison with a spindle (11) a shaft (41) which is supported by a support (50) so as to rotate freely and on the outer circumferential surface of which an external thread is formed an internal thread part (42) through which the shaft passes a stopper (43) for stopping the rotation of the internal thread part an abutting part (44) which moves together with the internal thread part that advances and retracts in the axial direction of the shaft as a result of the rotation of the shaft and abuts against the operating arm on the movement path and a handle (45) for rotating the shaft.
