Abstract: A bend detector for detecting a bend in headed rod members such as nails, screws, bolts, rivets and terminals. A guide plate, a base plate and a beam are mounted on a base which is being vibrated. Thus, a nail set in the bend detector is vibrated and rolls on the inclined edge of the guide plate and the base plate, which extends parallel to the edge of the guide plate. An air blower is provided under the head of the nail to lift it up from the edge of the guide plate by blowing air. If the nail is straight, it can roll smoothly on the edge of the guide plate and the base plate without its head disengaging from the edge of the guide plate even though it is lifted up from the edge of the guide plate by the air blower. If the nail is bent, its head will jump up until its shank abuts the beam when the crest of the bent portion faces downward while the nail is rolling. Its head will thus disengage from the edge of the guide plate, so that the nail will drop into the gap between the guide plate and the base plate.