Provided is a tracked running gear device in which attachment structure of a track roller for a track frame is improved. The tracked running gear device is provided with a drive sprocket (21) disposed at the front of a track frame (20) supported by a chassis frame (3), a tracked running gear belt (26) looped around a tension sprocket (22) disposed at the rear of the track frame (20), and a plurality of track rollers (23) which guide the tracked running gear belt (26) with respect to the ground. An attachment member (6) disposed on the track frame (20) is provided with an attachment unit (60) which is detachably attached and extends in the longitudinal direction of the chassis. The attachment unit (60) provides bearing support for multiple units of the track rollers (23) which are lined up in the vehicle body longitudinal direction.