Human error, an important factor, may lead to serious results in various operational fields. The human factor plays a critical role in the risks and hazards of the maritime industry. A ship can achieve safe navigation when all operations in the engine room are conducted vigilantly. This paper presents a systematic evaluation of 20 failures in auxiliary systems of marine diesel engines that may be caused by human error. The Cognitive Reliability Error Analysis Method (CREAM) is used to determine the potentiality of human errors in the failures implied thanks to the answers of experts. Using this method, the probabilities of human error on failures were evaluated and the critical ones were emphasized. The measures to be taken for these results will make significant contributions not only to the seafarers but also to the ship owners.