This paper presents an human reliability assessment(HRA) for a installation task of the temporary power cable in construction fields. HRA is evolved to ensure that the workers could reliably perform critical tasks such as a process of the temporary power cable. Human errors are extremely commonplace, with almost everyone committing at least some errors every day. The considerable parts of electric shock accidents in the construction field are caused by a series of human errors. Therefore it is required to analyze the human errors contained in the task causing electric shock event, the event tree analysis(ETA) is adopted in this paper, and particularly human reliability was estimated for a installation task of the temporary power cables. It was assumed that the error probabilities of the human actions may be obtained using the technique for human error rate prediction(THERP). The results show that the predominant task on reliability in the cable installation tasks is check-out tasks and the probability causing electric shock by human errors was calculated as $1.0 imes10^{-9}$