Provided is an acoustic insulation device for a mobile vehicle in which sound transmitted to the exterior of the vehicle body is blocked by being reflected or diffracted by acoustic insulation bodies provided upright to the vehicle body; and the amount of noise that an observer or local residents are subjected to is further reduced. Movement of a mobile vehicle generates noise in, and in the vicinity of, a power collector or a similar device provided upright on the roof (3) of the vehicle. Acoustic insulation bodies (1L), (2L), (1R), (2R) are provided upright on the roof (3), and block noise travelling directly ahead. The noise is diffracted or reflected by the acoustic insulation bodies (1L), (2L), (1R), (2R), and moves so as to be transmitted to the vehicle exterior. However, a branched, blade-shaped acoustic insulation body (1LB) provided to the acoustic insulation body (2L), or branched acoustic insulation bodies (1RB1), (1RB2) provided to the acoustic insulation body (2R), act on the diffracted or reflected noise to block sound, and therefore makes it possible to provide an acoustic insulation device for a mobile vehicle in which transmission to the outside of the vehicle body is minimized and the resulting noise is reduced.