To provide a belt sander in which a part of a polishing belt stretched around a front roller is sufficiently covered for securing proper protection in polishing a subject member as a plane, and in which limitation in polishing the subject member as a recessed surface is released to polish the subject member as the recessed surface effectively utilizing a curved surface of the front roller.

This belt sander is provided with a front roller 2, a back roller 3 disposed at an interval from that, a polishing belt stretched around the front roller 2 and the back roller 3, and a protective cover 5 for partially covering the stretched polishing belt 4. The protective cover 5 is provided with a movable cover 7 provided to be opened/closed to be capable of covering the front roller 2 above and in front of it. By releasing the movable cover 7, a surface of an exposed part of the polishing belt 4 stretched around the front roller 2 can be increased.