In a parking assist method, a surrounding image that is a color image obtained by capturing surroundings of an own vehicle is acquired, the surrounding image is converted to a first multi-gradation image in such a way that a luminance difference between a region in which a ratio of a green component is low and a region in which the ratio of the green component is high in the surrounding image increases, a feature point is extracted from the first multi-gradation image, and a relative position of the own vehicle with respect to a target parking position is calculated based on the extracted feature point.
