To provide a guide roller device of a belt conveyor for preventing the lateral travel of a conveyor belt from the predetermined moving direction and its reverse travel against a conveyor support structure.

The lower trunk of a belt is guided between a pair of guide rollers 12a, 1 2b rotatably arranged on the vertical shaft of a guide device 10, and a rotary shaft extended vertically to the surface of the belt is formed on the guide device 10 rotatably by the guide rollers 12a, 12b. The guide rollers 12a, 12b are installed on the brackets 11 of the guide device 10, and the rotary shaft is formed with a cylindrical member fixed with the brackets 11. Guide rollers 18, 19 in the advance direction of the lower trunk in the front of the guide rollers 12a, 12b and on both sides of the lower belt trunk are rotatably fixed to the guide device 10.