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 ope
