A vehicle attitude angle calculating device, comprising: a dividing line detection unit configured to detect a dividing line from image information received from a vehicle-mounted imaging device having an optical axis, the image information being a captured image of an outside of a vehicle; a distance calculation unit configured to calculate a distance between the dividing line and the optical axis of the vehicle-mounted imaging device every predetermined processing period; and a vehicle angle calculation unit, wherein the vehicle angle calculation unit includes: a dividing line angle calculation unit configured to calculate the dividing line angle on the basis of the calculated distance between the dividing line and the optical axis of the vehicle-mounted imaging device and the vehicle proceeding distance where the vehicle proceeds during a predetermined processing period; and a vehicle yaw angle calculation unit configured to calculate a yaw angle of the vehicle with reference to the dividing line on the basis of the calculated dividing line angle, characterized in that the dividing line includes a pair of left and right lines residing on left and right of the vehicle, and the distance between the dividing line and the optical axis of the vehicle-mounted imaging device includes a distance between the left line and the optical axis of the vehicle-mounted imaging device and a distance between the right line and the optical axis of the vehicle-mounted imaging device, wherein the dividing line angle calculation unit is configured to determine whether, among distances between the dividing line and the optical axis of the vehicle-mounted imaging device calculated by the distance calculation unit, a latest distance has been calculated or not, when it is determined that the latest distance has been calculated, the dividing line angle calculation unit is configured to determine whether, among a plurality of distances between the dividing line and the optical axis of the vehicle-mounted imaging device calculated by the distance calculation unit, a predetermined first number of distances or more have been calculated or not, and when it is determined that the predetermined first number of distances or more have been calculated, the dividing line angle calculation unit is configured to calculate the dividing line angle on the basis of the calculated plurality of distances. a dividing line detection unit configured to detect a dividing line from image information received from a vehicle-mounted imaging device having an optical axis, the image information being a captured image of an outside of a vehicle; a distance calculation unit configured to calculate a distance between the dividing line and the optical axis of the vehicle-mounted imaging device every predetermined processing period; and a vehicle angle calculation unit, wherein the vehicle angle calculation unit includes: a dividing line angle calculation unit configured to calculate the dividing line angle on the basis of the calculated distance between the dividing line and the optical axis of the vehicle-mounted imaging device and the vehicle proceeding distance where the vehicle proceeds during a predetermined processing period; and a vehicle yaw angle calculation unit configured to calculate a yaw angle of the vehicle with reference to the dividing line on the basis of the calculated dividing line angle, a dividing line angle calculation unit configured to calculate the dividing line angle on the basis of the calculated distance between the dividing line and the optical axis of the vehicle-mounted imaging device and the vehicle proceeding distance where the vehicle proceeds during a predetermined processing period; and a vehicle yaw angle calculation unit configured to calculate a yaw angle of the vehicle with reference to the dividing line on the basis of the calculated dividing line angle, the dividing line includes a pair of left and right lines residing on left and right of the vehicle, and the distance between the dividing line and the optical axis of the vehicle-mounted imaging device includes a distance between the left line and the optical axis of the vehicle-mounted imaging device and a distance between the right line and the optical axis of the vehicle-mounted imaging device, wherein the dividing line angle calculation unit is configured to determine whether, among distances between the dividing line and the optical axis of the vehicle-mounted imaging device calculated by the distance calculation unit, a latest distance has been calculated or not, when it is determined that the latest distance has been calculated, the dividing line angle calculation unit is configured to determine whether, among a plurality of distances between the dividing line and the optical axis of the vehicle-mounted imaging device calculated by the distance calculation unit, a predetermined first number of distances or more have been calculated or not, and when it is determined that the predetermined first number of distances or more have been calculated, the dividing line angle calculation unit is configured to calculate the dividing line angle on the basis of the calculated plurality of distances.