A vehicle attitude angle calculating device finds a yaw angle of a vehicle with reference to a lane stably without using information on a road vanishing point even in the state where a vehicle pitch angle varies. The vehicle attitude angle calculating device includes: a dividing line detection unit that detects a dividing line from image information received from a vehicle-mounted imaging device, the image information being a captured image of an outside of a vehicle; a distance calculation unit that calculates 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 that calculates a dividing line angle based on the calculated distance between the dividing line and the optical axis of the vehicle-mounted imaging device and a vehicle proceeding distance where the vehicle proceeds during a predetermined processing period.