A posture-change determining device comprising: an image acquiring unit configured to acquire a plurality of periphery images in which a periphery of a vehicle is imaged by a plurality of imaging devices that are provided facing front, back, left and right in the vehicle; characterized by a posture-change determining unit configured to determine whether a posture of the vehicle has changed, a control unit configured to cause the posture-change determining unit to identify intersections of straight lines as vanishing points (PA,PB), the straight lines extending toward a depth direction in the periphery images, acquire a variation of a tilt angle of the imaging device corresponding to a difference in a height direction between the vanishing points (PA,PB), calculate a variation of a height of the imaging device by extracting a movement vector expressing a change of position of a feature point in the periphery images, and calculate a variation of a rotation angle of the imaging device based on a variation of a tilt angle of the other imaging device facing in a different direction and a variation of a height of the other imaging device, to determine whether the posture of the vehicle has changed under a condition that a posture of at least one of the imaging devices has changed, wherein a convergent position at which the straight lines converge is the vanishing point at which a plurality of imaged objects that linearly extend in a direction parallel to a contact ground surface with which the vehicle is in contact intersect when extended in the periphery images, and the imaged object is at least one of a road marking, an installed item on a road, and a building. an image acquiring unit configured to acquire a plurality of periphery images in which a periphery of a vehicle is imaged by a plurality of imaging devices that are provided facing front, back, left and right in the vehicle; characterized by a posture-change determining unit configured to determine whether a posture of the vehicle has changed, a control unit configured to cause the posture-change determining unit to identify intersections of straight lines as vanishing points (PA,PB), the straight lines extending toward a depth direction in the periphery images, acquire a variation of a tilt angle of the imaging device corresponding to a difference in a height direction between the vanishing points (PA,PB), calculate a variation of a height of the imaging device by extracting a movement vector expressing a change of position of a feature point in the periphery images, and calculate a variation of a rotation angle of the imaging device based on a variation of a tilt angle of the other imaging device facing in a different direction and a variation of a height of the other imaging device, to determine whether the posture of the vehicle has changed under a condition that a posture of at least one of the imaging devices has changed, wherein a convergent position at which the straight lines converge is the vanishing point at which a plurality of imaged objects that linearly extend in a direction parallel to a contact ground surface with which the vehicle is in contact intersect when extended in the periphery images, and the imaged object is at least one of a road marking, an installed item on a road, and a building.