This control system is provided with: a position detection device that detects the position of a work machine; a noncontact sensor that detects an object around the work machine in a contactless manner; a position calculation unit that calculates the position of the work machine at least on the basis of map data indicative of the position of the object and detection data obtained by the noncontact sensor; and a diagnosis unit that compares the position of the work machine derived from the detection data of the position detection device with the position of the work machine calculated by the position calculation unit so as to make a diagnosis as to whether a defect is found in either the detection data of the position detection device or the calculation result of the position calculation unit.