The present invention employs a multi-link to an excavator for the first, and restricts a relative movement of the center frame (10) and the roller frame (20) using a multi-link bridge (30) in relation to an undercarriage system of vehicle body structures of the excavator. According to the present invention, in an undercarriage system in which the center frame 10 and the roller frame 20 are independently from each other, a plurality of links is added to rotate up and down by a predetermined angle in a vertical direction and a longitudinal direction of the roller frame (20) and thus the overturning can be prevented and also operator's feeling of riding can be enhanced by preventing an inclination of the center frame (10) due to condition of an uneven road surface, and a service life of the track can be increased as the partial wear is prevented.