[0001] The present invention relates to a working vehicle such as a tractor. [BACKGROUND ART] [0002] Patent document 1 is known as disclosing a technique for creating an agricultural work plan for an agricultural machine such as a tractor. An agricultural support system of Patent document 1 includes a server, a work instruction unit, an acquisition unit, and a display unit. The server includes a working menu storage portion that stores working menus including agricultural fields, agricultural workings, and dates of implementation. The work instruction unit transmits the working menus to an external party. The acquisition unit acquires the working menus transmitted by the work instruction unit. The display unit displays a list of the working menus including the agricultural fields, agricultural workings, and respective dates of implementation. [0003] In addition, Patent document 2 is known as disclosing a technique in which a camera is mounted on an agricultural machine. An autonomous traveling system for a working vehicle in Patent document 2 has a camera that takes images of the front of the vehicle and a controller that performs a steering control based on the images taken by the camera. [RELATED ART DOCUMENTS] [PATENT DOCUMENTS] _[flOO_4]_., . _ [Patent document 1] Japanese Unexamined Patent Application Publication No. 2018-110037 [Patent document 2] Japanese Unexamined Patent Application Publication No. 2017-117257 [DISCLOSURE OF THE INVENTION] [PROBLEMS TO BE SOLVED BY THE INVENTION] [0005] As described above, the agricultural support system of Patent document 1 is configured to manage the working menus including the agricultural fields, the agricultural workings, and the dates of implementation in performing the agricultural workings with the agricultural machine or the like; however, the system is not configured to know results of ground workings when the agricultural workings are actually performed. Although the agricultural support system can perform time management in the agricultural workings, the system cannot know or analyze the results of the ground workings when the agricultural workings are actually performed, that is, how the ground surfaces are. [0006] On the other hand, as shown in the autonomous traveling system of Patent document 2, the document discloses a technique to mount a camera on an agricultural machine and takes images showing results of traveling of the agricultural machine; however, the autonomous traveling system is only a system that controls the traveling based on the images taken by the camera and does not manage the results of ground workings. That is, the conventional technique only manages the time of agricultural working, and actually does not argue about how to know the results of ground workings. [0007] Thus, in view of the above-mentioned problems, the present invention intends to provide a working vehicle capable of easily acquiring results of ground workings when a ground working device performs ground workings. [MEANS OF SOLVING THE PROBLEMS] [0008] Technical means of the present invention for solving this technical problem is characterized by the following points. A working vehicle includes a vehicle body configured to be travelable, a ground working device attached to the vehicle body and configured to perform ground working, an imaging device located on the vehicle body and configured to image a ground working result after the ground working by the ground working device, and a storage configured to store a ground working image representing the ground working result taken by the imaging device. [0009] The working vehicle includes a first data acquisition unit configured to acquire the ground working image and operation information of the vehicle body. The storage stores the ground working image and the operation information acquired by the first data acquisition unit. The working vehicle includes a second data acquisition unit configured to acquire the ground working image and operation information of the ground working device. The storage stores the ground working image and the operation information acquired by the second data acquisition unit. [0010] The working vehicle includes a display configured to display the ground working image including the ground working result. The imaging device images, as the ground working result, a ground surface condition after the ground working. The working vehicle includes a working grading unit configured to grade the ground working based on the ground working image taken by the imaging device. [0011] The working grading unit performs the grading based on a first ground surface condition obtained from the ground working image after the ground working and a second ground surface condition serving as a reference for the ground working. The working vehicle includes a display configured to display a grading result graded by the working grading unit. The working vehicle includes a controller configured to change, based on the ground working image, a traveling condition of the vehicle body or the ground working to be performed by the ground working device. [EFFECTS OF THE INVENTION] * [0012] According to the present invention, results of ground working performed by a ground working device can be easily obtained. [BRIEF DESCRIPTION OF THE DRAWINGS] [0013] FIG7T~is a view illustrating a configuration of a working machine and a controfbloclT diagram. FIG. 2 is a perspective view of a lifting device. FIG. 3 is an explanation view explaining steering. FIG. 4 is a view illustrating a position of an imaging device. FIG. 5 is a view illustrating a relationship between a working area Wl and an imaging area of the imaging device. FIG. 6 is a view illustrating an example of an imaging screen Ml. FIG. 7A is a view illustrating an example of ground working performed by a rotary cultivator. FIG. 7B is a view illustrating an example of ground working performed by a plow. FIG. 7C is a view illustrating an example of ground working performed by a ridger. FIG. 8A is a view illustrating an example of grading to the rotary cultivator. FIG. 8B is a view illustrating an example of grading to the plow. FIG. 8C is a view illustrating an example of grading to the ridger. FIG. 9 is a view illustrating an example of a grading screen M2. FIG. 1.0 is a flowchart of changing a traveling condition of a vehicle body in the ground working. FIG. 11 is an explanation view explaining un cultivated field. FIG. 12 is a whole view of a tractor. [BEST MODE FOR CARRYING OUT THE INVENTION] [0014] With reference to the drawings, an embodiment of the present invention will be described below. FIG. 12 shows a control block diagram of a working machine. The working machine is an agricultural machine such as a tractor, a combine harvester, and a rice transplanter. The tractor will be employed as an example to explain the working machine. As shown in FIG. 12, a tractor 1 is provided with a vehicle (referred to as a vehicle body) 3 having a traveling device 7, a prime mover 4, and a transmission device 5. The traveling device 7 has front wheels 7F and rear wheels 7R. The front wheels 7F may be of tire type or crawler type. The rear wheels 7R may also be of the tire or crawler type. The prime mover 4 is a diesel engine, an electric motor, or the like, and in this embodiment the prime mover 4 iis constituted of the diesel engine. The transmission device 5 is configured to select a speed of rotation propelling the traveling device 7 through gear shifting, and is configured to switch the traveling direction of the traveling device 7 between forward traveling and backward traveling. A cabin 9 is located on the vehicle body 3, and a driver seat 10 is provided inside the cabin 9. [0015] On a rear portion of the vehicle body 3, a lifting device 8 is located, which is constituted of a three-point linkage mechanism or the like. A ground working machine 2 is capable of being attached to/detached from the lifting device 8. When the ground working machine 2 is attached to the lifting device 8, the ground working machine 2 can be towed by the vehicle body 3. The ground working device 2 is configured to perform workings on soil (that is, a ground surface) of an agricultural field and change a shape of the ground surface. The ground working device 2 is, for example, a cultivator, a ground leveler, a crusher, a ridger, or the like. In particular, the ground working machine 2 is a rotary cultivator, a subsoiler, a plow, a short disc, a power harrow, a ploughing machine, a ridger, or the like. In FIG. 12, an example is shown in which a cultivator is attached to as the ground working device 2. [0016] As shown in FIG. 1, the transmission device 5 is provided with a main shaft (that is, a propulsion shaft) 5a, a main transmission 5b, a sub transmission 5c, a shuttle unit 5d, a PTO power transmission 5e, and a front gear transmission 5f. The propulsion shaft 5a is rotatably supported by a housing case of the transmission device 5, and a power from a crankshaft of the engine 4 is transmitted to the propulsion shaft 5a. The main transmission 5b has a plurality of gears and a shifter (or shifters) configured to change connections between the gears. The main transmission 5b changes inputted rotation of the propulsion shaft 5a and outputs the rotation (changes a speed of the rotation) by selecting suitable gears to be drivingly connected (or engaged) with the shifter (or shifters). [0017] Similar to the main transmission 5b, the sub transmission 5c has a plurality of gears andlfsHrft'eF(oirsKrfters) configuredTxTchange connections between th^gears^ The7 sub transmission 5c changes inputted rotation of the main transmission portion 5b and outputs the rotation (changes a speed of the rotation) by selecting suitable gears to be drivingly connected (or engaged) with the shifter (or shifters). The shuttle unit 5d has a shuttle shaft 12 and a reverser 13. Power output from the sub transmission portion 5c is transmitted to the shuttle shaft 12 through the gears and the like. The reverser 13 constituted of, for example, a hydraulic clutch, and switches a rotational direction of the shuttle shaft 12, that is, selects either forward traveling or backward traveling of the tractor 1, by engaging and disengaging the hydraulic clutch. The shuttle shaft 12 is connected to a rear wheel differential device 20R. The rear wheel differential device 20R rotatably supports rear axles 21R to which the rear wheels 7R are attached. [0018] The PTO power transmission 5e has a PTO propulsion shaft 14 and a PTO clutch 15. The PTO propulsion shaft 14 is rotatably supported and is capable of transmitting a power from the propulsion shaft 5a. The PTO propulsion shaft 14 is connected to the PTO shaft 16 through gears or the like. The PTO clutch 15 is constituted of a hydraulic clutch or the like and is switched between a state in which a power of the propulsion shaft 5a is transmitted to the PTO propulsion shaft 14 and a state in which the power of the propulsion shaft 5a is not transmitted to the PTO propulsion shaft 14 by engaging and disengaging the hydraulic clutch.