A chute turning restriction mechanism includes: a rotary shaft on which a chute is disposed and which is provided to be capable of rotating relative to a vehicle body of a mixer truck; a bracket that is provided on the vehicle body and includes an insertion hole into which the rotary shaft is inserted and a cutaway portion formed by cutting away a part of the insertion hole; an inner diameter adjustment shaft provided across the cutaway portion to be capable of adjusting an inner diameter of the insertion hole, and configured to restrict rotation of the rotary shaft by reducing the inner diameter of the insertion hole; a rotary body that is provided to rotate together with the rotary shaft and includes an engagement groove; and a lock lever that is provided to be capable of rotating about the inner diameter adjustment shaft, and that restricts the rotation of the rotary shaft by engaging with the engagement groove.