1. A crosswalk detection device comprising: calculating unit that calculates, while moving a main pattern including a first sub pattern corresponding to white patterns of a crosswalk appearing in an image and a second sub pattern corresponding to a region between the white patterns from a first position on the image to a second position different from the first position, a first calculated value calculated based on brightness of pixels overlapping the first sub pattern and a second calculated value calculated based on brightness of pixels overlapping the second sub pattern; computing unit that performs arithmetic processing using the first calculated value and the second calculated value; and determining unit that determines whether or not an image of the crosswalk is present between the first position and the second position based on a regularity of a relationship between a position of the main pattern and a process result by the computing unit.