A suction orifice of a suction machine adapted to suck refuse from the ground and comprising: a channel adapted to be placed directly in contact with the external refuse to be sucked in, and wherein said channel is defined partly by a casing of metal material and partly by the ground; an inlet opening adapted to enable said refuse to enter said suction machine; a choking element adapted to vary the area of said inlet opening and consisting of a prismatic shell having a triangular base and an axis parallel to the ground and perpendicular to the flow direction when in use, the prismatic shell comprising an obstruction surface, a second upper face and a base surface; a hinge, comprising a rotation axis parallel to said ground and disposed at the corner opposite to said obstruction surface, suitable to fasten, in an idle manner, said choking element to said casing, so as to let the refuse impacting on said base surface (Sc) and, while moving forward, actuating said chocking element disposing it to the open position or to an intermediate position, causing an automatic variation of said area of said inlet opening according to the size of said refuse; characterised in that said channel comprises a first portion extending from an outer front opening to said inlet opening and converging from said outer front opening to said inlet opening only along section planes parallel to said ground, and said suction orifice comprises actuating means for the choking element, said actuating means acting on a bracket rigidly connected to said choking element and being operated by an operator, who can, in use and at all events, control the position of said choking element. a channel adapted to be placed directly in contact with the external refuse to be sucked in, and wherein said channel is defined partly by a casing of metal material and partly by the ground; an inlet opening adapted to enable said refuse to enter said suction machine; a choking element adapted to vary the area of said inlet opening and consisting of a prismatic shell having a triangular base and an axis parallel to the ground and perpendicular to the flow direction when in use, the prismatic shell comprising an obstruction surface, a second upper face and a base surface; a hinge, comprising a rotation axis parallel to said ground and disposed at the corner opposite to said obstruction surface, suitable to fasten, in an idle manner, said choking element to said casing, so as to let the refuse impacting on said base surface (Sc) and, while moving forward, actuating said chocking element disposing it to the open position or to an intermediate position, causing an automatic variation of said area of said inlet opening according to the size of said refuse; characterised in that said channel comprises a first portion extending from an outer front opening to said inlet opening and converging from said outer front opening to said inlet opening only along section planes parallel to said ground, and said suction orifice comprises actuating means for the choking element, said actuating means acting on a bracket rigidly connected to said choking element and being operated by an operator, who can, in use and at all events, control the position of said choking element.