The use of thresher machines for threshing rice plants helped farmers in improving agricultural productivity. However, thresher machine design that is currently available has not fairly concerned on the working position and posture of the farmers using it. The working position that was modeled by farmers when operating a thresher machine tent to cause injury because of the dimensions of the engine and the body of farmers that did not conform to each other. RULA method was one of the methods that could analyze work postures. From the results of the data collection and the process using RULA method, it was clear that the measures that had to be taken to the thresher machines which used to be available were promptly modified in order to avoid musculoskeletal problem. Improvements that could be undertaken to avoid the musculoskeletal problem on farmers who used the thresher machine were redesigning the thresher machine based on farmers working posture. One of these ways was by adjusting the dimensions of the farmers' body with the dimensions of the machine. In addition, the use of adjustable concept in the design could probably assist the farmers adjust the working position with the machinery they used.