Abstract- Isolation can results in such extreme states of mind as suicidal ideation, which are sometimes experienced by patients of psychiatric disorder (e.g. depression). We investigated when or why we feel a sense of isolation in the physical proximity of others, using a money game without any aspect of interest payments. 3subjects of the same sex took part in a “ lend and pay back money game” one of them, designated by the experimenter, was “betrayed” by other subjects. Under the condition in which the subjects represented their trust in others when they lent money, they felt loneliness (but not sadnees) when they were betrayed. Thus, we could replicate the feeling of loneliness through this procedure. This result may suggest that the sense of loneliness is associated with trust in and from others. This study showed the importance of interaction with others and its effects on both mental and physical well-beings. There results suggeset a possible correlation with and a model system of psychiatric disorder symptoms. Keywords-loneliness; sadness; trust