To accurately detect the roll state of a vehicle.

This roll detector 10 is constituted of a strain gauge 2D detecting the strain of a shock absorber 5D provided between a wheel D and a car body (not shown in the figure) and a CPU 1 judging the presence or absence of the roll transient state of a vehicle based on the detected value of the gauge 2D. Absorbers (not shown in the figure) are provided between other wheels and the car body, and the detected values of the gauges stuck to the absorbers are also inputted to the CPU 1. The absorber 5D is applied with the compressive force by the vertical downward force by the car body weight and the vertical upward reaction force in the grounded state of the wheel D, and it is applied with the tensile force by the weight of the wheel D when the wheel D is floated from the road surface. When the detected value of the gauge 2D is used, whether the wheel D is grounded or floated from the road surface can be detected, and the presence or absence of the roll transient state of the vehicle can be judged by combining them.