It has been desired to reduce the risk of the grains leaking out when the grain tank is in a state capable of being stored while making it easy to perform maintenance work inside the grain tank. The side plate 31 in the grain tank 7 rotates around the longitudinal center with respect to the tank main-body part 32, and the closed state which closes the opening 35 formed in the tank main-body part 32, and the outside A lock member 69 is provided so as to be switchable to an open state, the seal member 81 is provided at the periphery of the opening 35, and locks the side plate 31 in the closed state from the open state to the closed state. In accordance with being switched, it is possible to enter into the storage space through the opening 35 to a position corresponding to the locking member 70, and to the part through which the lock hole 69 in the sealing member 81 passes. In the position adjacent to the tank inner side, a restricting portion 82 is provided for restricting the lock mouth 69 from entering the tank inner side. The side plate 1031 in a grain tank is provided so that switching to a closed state and an open state is possible by rotating about the longitudinal axis of the tank main body part 1032, and hold maintains the position which keeps the side plate 1031 in the closed state. The mechanism IH is provided with a plurality of locking fixing portions 1063 and 1069 and a plurality of locking fixing portions 1040 and 1070, and an operating tool 1064 for switching and operating the plurality of locking fixing portions collectively. When the specific locking fixture 1063 is in the boundary position, the other locking fixture 1069 is in a position corresponding to the boundary position or the locking release state, and the specific locking fixture 1063 is in the boundary position. When the side plate 1031 is moved to the closed state side in the state which is located in the state more than the locked state, the specific locking part 1063 is prevented before
