In recent years, automation systems that conduct human physical and cognitive tasks on people’s behalf are coming to join our everyday life. In this article, first, we define automation systems as a third artifact, compared with primitive tools that support human physical activities and cognitive artifacts that support human cognitive activi- ties. Second, we review three branches of researches investigated in the research field of human-automation system interaction, and show the importance of the function of trust when making a relationship with automation systems. Finally, we show common- alities and differences in the nature of trust for human-human and human-automation system interaction.