To provide a simple and thin belt conveyor installed for industrial use or the like and capable of reducing management work for removing dropping dust from a return belt and maintaining a condition in which there is no dropping dust obstacle.

This belt conveyor is provided with an underpan 1 serving as three functions including those of a return roller, an underguard which is a receiver for dropping dust, and a dropping dust chute which are constituent elements of the conveyor. The underpan has such structure that an air supply box 7 in which an air supply pipe 5 having an injection hole 6 in substantially central part of conveyor width is arranged is provided to supply pressurized air through the air supply box in order to reduce friction resistance between the return belt and the underpan. Consequently, dropping dust of the return belt is conveyed to a tail part of the conveyor by a method for nipping it between the return belt and the underpan without increasing power load of the return belt.