It is intended to accurately calculate the distance between a movable body and a subject on the basis of various quantities of state, such as the azimuth angle between the movable body and the subject, velocity, and yaw rate. A calculation device includes a unit for calculating the azimuth angle between movable body and a subject, a unit for calculating the distance traveled by the movable body between two points of time, a unit for calculating a change in angle in the direction of movement, and a unit for calculating the linear distance from the movable body to the subject by using the unit.