A hopper attachment structure that allows a hopper to be attached to a driving unit, the hopper comprising: an outlet in a body thereof; and a gate (7b, 7c) driven to open and close by the driving unit, the outlet of the hopper being allowed to open and close with the gate (7b, 7c), the driving unit comprising an engaging protrusion (28, 29), the hopper further comprising an attachment bracket extending from the body, the attachment bracket comprising: a hook portion engageable with the engaging protrusion (28, 29); and wherein the driving unit further comprises a support protrusion, and the attachment bracket comprises a contact portion allowed to contact the support protrusion, the hopper being removably attachable to the driving unit by having the hook portion of the attachment bracket engaged with the engaging protrusion (28, 29) of the driving unit and by further having the contact portion of the attachment bracket supportably contact the support protrusion of the driving unit, wherein the engaging protrusion (28, 29) is formed on each of lateral surfaces on both sides of the driving unit, the support protrusion is formed on each of the lateral surfaces, and a pair of the attachment brackets facing each other are extended from the body, characterised in that the engaging protrusion formed on one of the lateral surfaces of the driving unit is a boss portion that pivotally and rotatably supports a driving arm used to open and close the gate (7b, 7c). an outlet in a body thereof; and a gate (7b, 7c) driven to open and close by the driving unit, the outlet of the hopper being allowed to open and close with the gate (7b, 7c), the driving unit comprising an engaging protrusion (28, 29), the hopper further comprising an attachment bracket extending from the body, the attachment bracket comprising: a hook portion engageable with the engaging protrusion (28, 29); and wherein the driving unit further comprises a support protrusion, and the attachment bracket comprises a contact portion allowed to contact the support protrusion, the hopper being removably attachable to the driving unit by having the hook portion of the attachment bracket engaged with the engaging protrusion (28, 29) of the driving unit and by further having the contact portion of the attachment bracket supportably contact the support protrusion of the driving unit, wherein the engaging protrusion (28, 29) is formed on each of lateral surfaces on both sides of the driving unit, the support protrusion is formed on each of the lateral surfaces, and a pair of the attachment brackets facing each other are extended from the body, characterised in that the engaging protrusion formed on one of the lateral surfaces of the driving unit is a boss portion that pivotally and rotatably supports a driving arm used to open and close the gate (7b, 7c). a hook portion engageable with the engaging protrusion (28, 29); and wherein the driving unit further comprises a support protrusion, and the attachment bracket comprises a contact portion allowed to contact the support protrusion, the hopper being removably attachable to the driving unit by having the hook portion of the attachment bracket engaged with the engaging protrusion (28, 29) of the driving unit and by further having the contact portion of the attachment bracket supportably contact the support protrusion of the driving unit, wherein the engaging protrusion (28, 29) is formed on each of lateral surfaces on both sides of the driving unit, the support protrusion is formed on each of the lateral surfaces, and a pair of the attachment brackets facing each other are extended from the body, characterised in that the engaging protrusion formed on one of the lateral surfaces of the driving unit is a boss portion that pivotally and rotatably supports a driving arm used to open and close the gate (7b, 7c).