A step detection device detects the distance and the direction to a road surface around a vehicle, using a distance sensor mounted on the vehicle, and sets a first step determination position and a second step determination position on the road surface. Then, the step detection device calculates the height changes of the road surfaces at the first step determination position and the second step determination position based on the distance and the direction to the road surface, and detects a step on the road surface based on one of the step determination positions, the gradient of the height change of the road surface at the one being larger.