A vehicle monitoring device includes a positioning device, a distance calculator, a first imaging device, a volume calculator, and a work calculator. The positioning device measures a position of a vehicle including a loading platform. The distance calculator calculates a movement distance of the vehicle based on the position of the vehicle measured by the positioning device. The first imaging device captures an image of a load mounted on the loading platform. The volume calculator calculates a volume of the load based on the image captured by the first imaging device. The work calculator calculates a work of the vehicle based on the movement distance and the volume of the load.