Flatness detection device

The invention discloses a flatness detection device, and belongs to the field of detection devices. The device comprises: a shell provided with an inner gear ring; a rotating wheel is rotatably arranged in the shell, a fixing hole used for fixing a detection instrument is formed in the rotating wheel, the rotating wheel and the inner gear ring are coaxially arranged, and the fixing hole and the inner gear ring are eccentrically arranged; and a transmission device is arranged between the inner gear ring and the rotating wheel and is used for keeping the display surface of the detection instrument towards the same direction all the time when the rotating wheel rotates. When the rotating wheel rotates, the detection instrument rotates synchronously, due to the fact that the fixing hole andthe inner gear ring are eccentrically arranged, when the rotating wheel rotates by one circle, the detection instrument revolves by one circle around the axis of the inner gear ring, and due to the fact that the whole oil seal