A road surface gradient detection device is provided. The road surface gradient detection device includes an image area setting unit configured to divide a captured image to set a plurality of image areas, a weighting setting unit configured to set the weighting of the pixel range, a representative height calculation unit configured to calculate the representative parallax of each image area and the representative height of each image area based on the parallax of each pixel range, the coordinates of each pixel range, and a magnitude of the weighting of each pixel range, and a road surface gradient detection unit configured to detect the road surface gradient from the captured image based on the representative parallax of each image area and the representative height of each image area.