An information processing system includes a state estimation section that estimates a state of a user based on information that includes sensor information from at least one of a behavior sensor that measures a behavior of the user, a condition sensor that measures a condition of the user, and an environment sensor that measures an environment of the user, a historical information storage section that stores state historical information about the user, a usualness level evaluation section that evaluates a usualness level of the user, and a write section that writes the usualness level of the user evaluated by the usualness level evaluation section in the historical information storage section so that the usualness level is linked to each state of the user indicated by the state historical information about the user.