| CPC G01B 21/22 (2013.01) | 18 Claims |

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1. A trailer length estimation device configured to estimate, in a vehicle including a tractor and a trailer connected to the tractor by a connecting device, a trailer length from the connecting device to a wheel of the trailer, the trailer length estimation device comprising:
an acquisition unit configured to acquire a turning angle of a wheel of the tractor, and a connection angle of the trailer with respect to the tractor, the turning angle being detected by a turning angle detector, and the connection angle being detected by a connection angle detector; and
a derivation unit configured to:
calculate an amount of change in the acquired connection angle, and
derive the trailer length based on the acquired turning angle and the calculated amount of change in the acquired connection angle when the vehicle is making an unsteady turn.
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