A tractor comprising: a seat; a safety frame having two struts extended upward from right and left side portions rearward from the seat and formed in a reversed U-shape in rear view so as to have a lateral upper portion; a vehicle body frame including a pair of right and left longitudinal frames and lateral frames laid between the right and left longitudinal frames so as to have right and left outer surfaces; right and left attachment brackets fixed on both the right and left outer surfaces of the vehicle body frame; and a front frame having right and left lower portions detachably attached to the right and left attachment brackets, characterized in that the front frame is formed in a gate shape in front view so as to integrally have a pair of right and left front struts and a lateral upper portion extended between upper portions of the right and left front struts; that a pair of right and left roof frames separated from each other and from the safety frame and the front frame are detachably attached at front ends thereof with respective front coupling stays fixed thereon to the respective upper portions of the front struts at right and left portions of the lateral upper portion of the front frame via bolts, and at rear ends thereof with respective rear coupling stays fixed thereon to right and left portions of the lateral upper portion of the safety frame via bolts, so as to connect the lateral upper portion of the front frame to the lateral upper portion of the safety frame, and that each of the roof frames is provided with a roof attachment member on an outer surface thereof, so that a roof can be attached to the roof attachment members on the right and left roof frames. a seat; a safety frame having two struts extended upward from right and left side portions rearward from the seat and formed in a reversed U-shape in rear view so as to have a lateral upper portion; a vehicle body frame including a pair of right and left longitudinal frames and lateral frames laid between the right and left longitudinal frames so as to have right and left outer surfaces; right and left attachment brackets fixed on both the right and left outer surfaces of the vehicle body frame; and a front frame having right and left lower portions detachably attached to the right and left attachment brackets, characterized in that the front frame is formed in a gate shape in front view so as to integrally have a pair of right and left front struts and a lateral upper portion extended between upper portions of the right and left front struts; that a pair of right and left roof frames separated from each other and from the safety frame and the front frame are detachably attached at front ends thereof with respective front coupling stays fixed thereon to the respective upper portions of the front struts at right and left portions of the lateral upper portion of the front frame via bolts, and at rear ends thereof with respective rear coupling stays fixed thereon to right and left portions of the lateral upper portion of the safety frame via bolts, so as to connect the lateral upper portion of the front frame to the lateral upper portion of the safety frame, and that each of the roof frames is provided with a roof attachment member on an outer surface thereof, so that a roof can be attached to the roof attachment members on the right and left roof frames.