Conventionally, there is a vehicle travel control device including a function of following a preceding vehicle that travels in front of a host vehicle using a sensor, such as an in-vehicle radar or an in-vehicle camera.
As a vehicle travel control device mentioned above, there is a vehicle traveling state detection device for predicting, for example, sudden acceleration and deceleration of a preceding vehicle by accurately detecting an unstable travel state of the preceding vehicle. In the vehicle traveling state detection device, a preceding vehicle unstable situation determination means determines that the preceding vehicle is in an unstable situation when at least one of a degree of unsteadiness in a lateral direction of the preceding vehicle, a degree of bias in the traveling lane of the preceding vehicle, and an amount of lateral displacement per unit time of the preceding vehicle is a predetermined specified value or more, and the means can prompt the driver of the vehicle to drive accurately (for example, refer to PTL 1).