A travel sickness estimation system comprising: an input unit configured to receive output of a sensing system used to acquire vehicle information indicating conditions of a moving vehicle, and person information indicating conditions of a person who is on board the moving vehicle, an estimation unit configured to perform estimation processing of estimating, based on the person information, whether or not the person is in circumstances that would cause travel sickness for him or her, at the estimation processing, estimating whether the person is in circumstances that would cause travel sickness for him or her is estimating chances of triggering an onset of travel sickness for the person; and an output unit configured to output a result of the estimation processing performed by the estimation unit, the estimation unit being configured to perform the estimation processing with reference to not only the person information but also the vehicle information, the person information including posture information indicating the person's posture, the vehicle information including behavior information indicating a behavior of the moving vehicle, characterized in that the person's posture being represented by a tilt angle defined by a center axis of the person's head with respect to a center axis of his or her body trunk and a tilt angle defined by the center axis of his or her body trunk with respect to a horizontal plane, the estimation unit being configured, in the estimation processing, to when finding a tilt angle or the moving vehicle's traveling direction or propulsion greater than their reference value, obtain a magnitude of a gap between the behavior of the moving vehicle and the person's posture to increase an estimated value about travel sickness according to the magnitude of the gap, and when the magnitudes of the gap between the behavior of the moving vehicle and the person's posture are accumulated to make the estimated value equal to or greater than a threshold value, make a determination that the person is in circumstances that would cause travel sickness for him or her an input unit configured to receive output of a sensing system used to acquire vehicle information indicating conditions of a moving vehicle, and person information indicating conditions of a person who is on board the moving vehicle, an estimation unit configured to perform estimation processing of estimating, based on the person information, whether or not the person is in circumstances that would cause travel sickness for him or her, at the estimation processing, estimating whether the person is in circumstances that would cause travel sickness for him or her is estimating chances of triggering an onset of travel sickness for the person; and an output unit configured to output a result of the estimation processing performed by the estimation unit, the estimation unit being configured to perform the estimation processing with reference to not only the person information but also the vehicle information, the person information including posture information indicating the person's posture, the vehicle information including behavior information indicating a behavior of the moving vehicle, characterized in that the person's posture being represented by a tilt angle defined by a center axis of the person's head with respect to a center axis of his or her body trunk and a tilt angle defined by the center axis of his or her body trunk with respect to a horizontal plane, the estimation unit being configured, in the estimation processing, to when finding a tilt angle or the moving vehicle's traveling direction or propulsion greater than their reference value, obtain a magnitude of a gap between the behavior of the moving vehicle and the person's posture to increase an estimated value about travel sickness according to the magnitude of the gap, and when the magnitudes of the gap between the behavior of the moving vehicle and the person's posture are accumulated to make the estimated value equal to or greater than a threshold value, make a determination that the person is in circumstances that would cause travel sickness for him or her when finding a tilt angle or the moving vehicle's traveling direction or propulsion greater than their reference value, obtain a magnitude of a gap between the behavior of the moving vehicle and the person's posture to increase an estimated value about travel sickness according to the magnitude of the gap, and when the magnitudes of the gap between the behavior of the moving vehicle and the person's posture are accumulated to make the estimated value equal to or greater than a threshold value, make a determination that the person is in circumstances that would cause travel sickness for him or her