Plugging-in of a wood piece for the culture of shiitake mushroom is one of machine-assisted works in forestry, and is achieved by the use of an electric drill. The purpose of this study is to evaluate the effects of this work on the psychophysiological functions of workers. The work consisted of two conditions ; working on a work table and working on the bare ground. The work load was examined by multifaceted observation. Results indicated that the CFF and the function of concentration (TAF-test) when compared with pre-work values were not significantly reduced after approximately 50 minutes of work. But the work perfonuance produced a local muscular load due to work in unnatural work postures and the workers feel fatigue due to work itself. However, working on the work table had effects on mitigation on the work load, shortening of the working time and improvement of the work postures.