In a dimension estimation device, an image acquired in a moving body is acquired, and a vanishing point and a predetermined decision line in the image are calculated. An object in the image is detected and a detection rectangle is detected for the object, the detection rectangle being a rectangle including a first surface that is a surface close to a photographing position, the first surface being in proximity to the decision line, and a second surface that is a surface far from the photographing position. A dimension of the object is estimated on the basis of a ratio between a height of the first surface and a height of the second surface obtainable from a relationship between the detection rectangle and the vanishing point.