The invention relates to a harvester, in particular to a threshing device of a harvester. According to the technical scheme, the threshing device of the harvester comprises an underframe, a threshing frame, a main threshing mechanism, a rethreshing mechanism, a separation, cleaning and vibration screen and an impurity lifting screw, wherein the threshing frame is fixed on the underframe, both the main threshing mechanism and the rethreshing mechanism are connected to the threshing frame and disposed along the travelling direction of the harvester, the separation, cleaning and vibration screen is fixedly connected to the threshing frame and positioned between the underframe and the main threshing and rethreshing mechanisms, and the impurity lifting screw is disposed between the position below the rear end of the separation, cleaning and vibration screen and the rethreshing mechanism. The main threshing mechanism comprises a main threshing roller, a large concave screen and a main roller cover, wherein the main threshing roller is hinged to the threshing frame, the large concave screen is fixed to the threshing frame and encloses the main threshing roller, and the main roller cover covers an opening of the large concave screen. The main threshing roller is slantingly disposed along the advancing direction of the harvester. A corner between the main threshing roller and a conveying chute of the threshing device compared with the prior art is reduced, so that conveying of crops is smooth, and the shortages of the prior art are made up.