A dump truck comprising: a frame; a plurality of rear wheels (15a, 15b, 15c, 15d) rotatably attached to the frame; a plurality of rear suspensions (17a, 17b) for suspending the frame at the plurality of rear wheels (15a, 15b, 15c, 15d); two GPS receivers (101, 102) disposed to be dislocated from each other in both an anteroposterior direction and a lateral direction of the dump truck, and that receive navigation signals from GPS satellites, a storage unit that stores maps in which shapes and gradients of a road for the dump truck are defined by a plurality of links, each of the plurality of links having a starting point and ending point indicated by three-dimensional coordinates at a ground coordinate system set on a ground, and a calculation device configured to calculate positions of two points corresponding to the two GPS receivers (101, 102) based on the navigation signals, and calculate the attitude of the dump truck based on the two points, characterized in that when any point in a vehicle coordinates system set at the dump truck is selected from areas where the rear wheels (15a, 15b, 15c, 15d) contact the ground in a vehicle coordinates system set at the frame is defined as a reference point, the two GPS receivers (101, 102) are disposed so that the reference point is normal to a line segment connecting the two points corresponding to the the two GPS receivers (101, 102), the calculation device: specifies a first link that the dump truck is traveling from the plurality of the links based on the positions of the two points, defines a vector SE from a starting point S and an ending point E of the first link, defines a normal direction vector crossing at a right angle with the vector SE on a traveling surface J including the first link as a vector NL, expresses a position of the reference point by using the vector SE and the vector NL, calculates the position of the reference point based on the positions of the two points, the vector SE and the vector NL by using that distances from the reference point to the two points which can be calculated in advance under an assumption that the attitude of the dump truck changes by rotating around the reference point, and calculates the attitude of the dump truck based on the positions of the two points and the reference point. a frame; a plurality of rear wheels (15a, 15b, 15c, 15d) rotatably attached to the frame; a plurality of rear suspensions (17a, 17b) for suspending the frame at the plurality of rear wheels (15a, 15b, 15c, 15d); two GPS receivers (101, 102) disposed to be dislocated from each other in both an anteroposterior direction and a lateral direction of the dump truck, and that receive navigation signals from GPS satellites, a storage unit that stores maps in which shapes and gradients of a road for the dump truck are defined by a plurality of links, each of the plurality of links having a starting point and ending point indicated by three-dimensional coordinates at a ground coordinate system set on a ground, and a calculation device configured to calculate positions of two points corresponding to the two GPS receivers (101, 102) based on the navigation signals, and calculate the attitude of the dump truck based on the two points, characterized in that when any point in a vehicle coordinates system set at the dump truck is selected from areas where the rear wheels (15a, 15b, 15c, 15d) contact the ground in a vehicle coordinates system set at the frame is defined as a reference point, the two GPS receivers (101, 102) are disposed so that the reference point is normal to a line segment connecting the two points corresponding to the the two GPS receivers (101, 102), the calculation device: specifies a first link that the dump truck is traveling from the plurality of the links based on the positions of the two points, defines a vector SE from a starting point S and an ending point E of the first link, defines a normal direction vector crossing at a right angle with the vector SE on a traveling surface J including the first link as a vector NL, expresses a position of the reference point by using the vector SE and the vector NL, calculates the position of the reference point based on the positions of the two points, the vector SE and the vector NL by using that distances from the reference point to the two points which can be calculated in advance under an assumption that the attitude of the dump truck changes by rotating around the reference point, and calculates the attitude of the dump truck based on the positions of the two points and the reference point. specifies a first link that the dump truck is traveling from the plurality of the links based on the positions of the two points, defines a vector SE from a starting point S and an ending point E of the first link, defines a normal direction vector crossing at a right angle with the vector SE on a traveling surface J including the first link as a vector NL, expresses a position of the reference point by using the vector SE and the vector NL, calculates the position of the reference point based on the positions of the two points, the vector SE and the vector NL by using that distances from the reference point to the two points which can be calculated in advance under an assumption that the attitude of the dump truck changes by rotating around the reference point, and calculates the attitude of the dump truck based on the positions of the two points and the reference point.