From an early age, children are generally familiar with non-human agents; robots are depicted in picture books or movies. However, little is known about whether young children attribute mental states for non-human agents similar to those for human agents. Forty-five young children aged 5 and 6 years old participated. Two types of standard false belief tasks were prepared. The only difference of the two tasks was the agent: human or robot. Stories were presented as animations. The results showed that most participants correctly answered the control questions in both tasks. However, for the belief questions, the percentage of the correct answers in the task of human agents was higher than that in the task of non-human agents. These results demonstrate that young children ages 5 or 6 are already sensitive to mental states of human agents, but not to non-human agents.