To provide a generator for recovering energy effectively, in a case where the vehicle decelerates, using a brake on a steep downhill or the like.

It is constituted such that a roller is embedded horizontally at an angle of 90 with respect to the direction of advance of a vehicle, in the surface of the earth, where a vehicle decelerates so as to allow tire to contact with the roller, and that the rotation of the roller is transmitted to rotate a generator for power generation. The roller and the generator are integrated into a cassette, and the device made into a cassette is embedded in a place, where there is much traffic and the brake of the vehicle is applied, and the repair and the replacement can be simplified with the replacement of the cassette generator. Moreover, the device can be made flat and placed on a road, too.