A step detection device comprising: a distance sensor which is mounted on a vehicle (Vc) and detects a distance and a direction to a road surface around the vehicle (Vc) from an installation position of the distance sensor on the vehicle (Vc); a step determination position circuit which sets a first step determination position on the road surface, the first step determination position being in a linear shape and being away from the distance sensor in a first predetermined direction by a first predetermined distance and extending in a direction orthogonal to the first predetermined direction, wherein the first predetermined direction is set to be a traveling direction of the vehicle (Vc), and which sets a second step determination position on the road surface, the second step determination position being in a linear shape and being away from the distance sensor in a second predetermined direction by a second predetermined distance and extending in a direction orthogonal to the second predetermined direction; a road surface height calculation circuit which calculates a height change of the road surface at the first step determination position and a height change of the road surface at the second step determination position, by acquiring a height of the road surface around the vehicle from the distance and the direction to the road surface detected by the distance sensor; characterized by the first predetermined direction and the second predetermined direction being set in a horizontal plane, wherein the second predetermined direction is different from the first predetermined direction; and a step existing area circuit which estimates a step existing area (Q1-Q3) including a road surface height changing portion at which the height of the road surface changes at the first step determination position, wherein the step determination position circuit sets the second step determination position passing through the step existing area (Q1-Q3); a step detection circuit which detects a step on the road surface by selecting one of the first step determination position and the second step determination position, a gradient of the height change of the road surface at the selected step determination position being larger than a gradient of the height change of the road surface at the other. a distance sensor which is mounted on a vehicle (Vc) and detects a distance and a direction to a road surface around the vehicle (Vc) from an installation position of the distance sensor on the vehicle (Vc); a step determination position circuit which sets a first step determination position on the road surface, the first step determination position being in a linear shape and being away from the distance sensor in a first predetermined direction by a first predetermined distance and extending in a direction orthogonal to the first predetermined direction, wherein the first predetermined direction is set to be a traveling direction of the vehicle (Vc), and which sets a second step determination position on the road surface, the second step determination position being in a linear shape and being away from the distance sensor in a second predetermined direction by a second predetermined distance and extending in a direction orthogonal to the second predetermined direction; a road surface height calculation circuit which calculates a height change of the road surface at the first step determination position and a height change of the road surface at the second step determination position, by acquiring a height of the road surface around the vehicle from the distance and the direction to the road surface detected by the distance sensor; characterized by the first predetermined direction and the second predetermined direction being set in a horizontal plane, wherein the second predetermined direction is different from the first predetermined direction; and a step existing area circuit which estimates a step existing area (Q1-Q3) including a road surface height changing portion at which the height of the road surface changes at the first step determination position, wherein the step determination position circuit sets the second step determination position passing through the step existing area (Q1-Q3); a step detection circuit which detects a step on the road surface by selecting one of the first step determination position and the second step determination position, a gradient of the height change of the road surface at the selected step determination position being larger than a gradient of the height change of the road surface at the other.